
Mass Q V 'h £ 

Book : 

Copyright^' 

COPYRIGHT DEPOSrr 



OUTLINES OF PHYSIOLOGY 
JONES 



OUTLINES 



OF 



PHYSIOLOGY 



Bv 



EDWARD GROVES JONES, M.D., 

LECTURER OX PHYSICAL DIAGNOSIS IN THE ATLANTA COLLEGE OF PHYSICIANS AND 

SURGEONS, AND PROFESSOR OF PHYSIOLOGY IN THE DENTAL 

DEPARTMENT OF THE SAME. 



107 ILLUSTRATIONS 




PHILADELPHIA : 
P. BLAKISTON'S SON & CO. 

IOI2 WALNUT STREET. 
I 90 I 






. 



V3 



The" library of 
congress, 

Two Comes Received 

NOV. 18 1901 

OOPVRIQMT ENTRy 

CLASS OSXXc Ho. 

/ ? $ JT K 
copy a 



Copyright, 190 1, 
P. Blakiston's Son & Co. 



TO 



DOCTOR WILLIAM S. KENDRICK, 

Professor of Medicine in the Atlanta College of Physi- 
cians and Surgeons, 

THESE PAGES ARE AFFECTIONATELY DEDICATED, 



J 



PREFACE. 

This volume has been prepared with the view of presenting, 
in as convenient form as possible, the essential facts of modern 
physiology as related to the practice of medicine. In the exe- 
cution of this purpose brevity has been made a prime considera- 
tion ; therefore, such details as are of secondary importance are 
omitted, theories are avoided, and conclusions are recorded 
without argument. There is no short road to knowledge, and 
it would be unfortunate should such a book as this in any way 
discourage extended research ; but students in college have none 
too much time to devote to any one subject, and any simple col- 
lection of pertinent facts, however brief, can, if reliable, be 
used to great advantage. I have endeavored, however, to make 
the work sufficiently exhaustive to be self-explanatory, believing 
that otherwise economy of expression is practiced at the expense 
of the reader's interest. 

A maximum of space has been given to those subjects which 
seem of most practical importance. The chemistry of the body, 
the special senses and embryology have not been treated in great 
detail. It has been thought undesirable to omit a brief anatom- 
ical description of the separate organs discussed. 

In the preparation of this volume no claim to original inves- 
tigation is made. The writings of various authorities have been 
freely drawn upon. Especial acknowledgment is due to the 
following authors: Howell (American Text-Book), Halliburton 
(Kirkes' Handbook), Flint, Verworn and Stewart. 

I am under obligations to Dr. J. Clarence Johnson, whose 
lectures have been of great value to me, and to Dr. Frank K. 
Boland, who has written the whole of Chapter II. , read the proof 
sheets, and rendered other valuable assistance in connection with 
the work. 

E. G. J. 

Atlanta, Ga., Sept. i, 1901. 



j 



INTRODUCTION. 



Human physiology treats of the occurrences which take place 
in the body of man during life. 

Life is indefinable. In discussing it we can at best only 
recount some of its invariable and characteristic phenomena. 
In the normal living body there is ability on the part of all tissues 
to perform their proper functions — functions which are termed 
physiological. In disease there is impairment of this ability on 
the part of some or all the tissues. In death there is irremediable 
loss of function throughout the organism, though such loss does 
not extend to all the tissues at the same moment of time. It 
therefore appears that we shall be concerned with a consideration 
of some of the conditions which distinguish living from dead 
matter, and with a description of some of the functions of the 
body and of its different parts. 

The vital processes are alike in character in plants and ani- 
mals, but only animal life is now under discussion. 

Distinguishing Characteristics of Living Matter. — It will be 
here considered that these are : ( i ) Motion, ( 2 ) irritability, 
(3) nutrition, (4) growth, (5) reproduction. As the character- 
istics of the living organism are characteristics of the living cell, 
attention is directed to p. 29 et seq., where the properties of 
cells are discussed. 

Functions to be Performed in the Body. — In the body there 
is a division of labor, whereby one organ is predominantly con- 
cerned in the performance of one function and others in the 
performance of distinctly different ones — the sum total of their 
activity being life and its attendant phenomena. Assuming that 



Xll INTRODUCTION. 

physiological activity has as its object the preservation and prop- 
agation of life and the accomplishment of certain acts peculiar 
to the animal, the functions of the body and its different parts 
maybe classified as, (I.) Nutritive, (II.) Animal and (III.) 
Reproductive. 

I. The Nutritive embrace a very large part of the physio- 
logical processes going on in the body. They are ( i ) secre- 
tion, (2) digestion, (3) absorption, (4) respiration, (5) circu- 
lation, (6) metabolism, (7) excretion, (8) production of heat. 
Their performance occurs involuntarily and unconsciously. 
They make the animal and reproductive functions possible. 

II. The Animal axe such as motion, speech, intellection, etc. 
Their performance may be said to be voluntary, but dependent 
upon the nutritive functions. 

III. The Reproductive involve the processes necessary to per- 
petuate the species. 

While the above remarks are meant to apply to the body as a 
whole, the organism consists only of an aggregation of specialized 
cells, and it is to be noted that all the functions classed above 
as nutritive and reproductive, and at least a part of those classed 
as animal, are properties of all living cells. 

" Vital Force.' f — The phenomena exhibited by living matter 
may be due largely to changes in the chemical and physical na- 
ture of protoplasm, and the ignorance of the day regarding 
physiological changes may be ignorance of the chemistry and 
physics of protoplasm. We differentiate objects in the inorganic 
world on chemical and physical grounds ; it may be that one 
form of living matter differs from another in its function on the 
same grounds. We know, for example, speaking broadly, that 
digestion takes place in accordance with known chemical laws ; 
that circulation is governed by the laws of hydrodynamics ; that 
respiration obeys laws of aerodynamics ; that absorption is; de- 
pendent upon osmosis ; that the skeletal movements are in ac- 
cordance with the principles of mechanics. 



-1 



INTRODUCTION. Xlll 

But it will be seen from time to time that many circumstances 
attending these processes, and many other manifestations of vital 
activity, cannot be explained by any known physical or chemical 
laws. All secretions come from blood or lymph, and yet these 
secretions may contain substances entirely different from any 
found in those fluids ; the epithelium of one gland may take out 
of the blood certain materials, while the apparently identical 
epithelium of another gland under apparently identical condi- 
tions will not do so ; absorption from the alimentary canal shows 
numerous variations from the laboratory laws of osmosis ; while 
investigation of the problems of heredity and consciousness can 
scarcely be said to have made a beginning. It will, therefore, 
be necessary to use frequently such terms as " vital force," " se- 
lective affinity," etc., but without any clear understanding of the 
processes they are supposed to describe. 

The contributions which recent years have made to the knowl- 
edge of physiology seem to be the result of investigations which 
look to physics and chemistry for explanation of at least some 
of the " vital" phenomena of life. It is hardly to be supposed 
that the application of these methods has reached its limit, and 
the hope may be indulged that some of the mysteries that now 
beset the study of physiology may be explained by perfectly well- 
known laws. It has been a comparatively short time since it was 
thought impossible to synthesize any of the so-called organic 
bodies. 

The subject of general physiology is the subject of cell physi- 
ology. The life of the cell is inherited ; its nutrition and activity 
depend on a proper supply of food (blood), proper physical sur- 
roundings, and (usually) proper nerve connections. Any change, 
whether constructive or destructive, in the cell is effected through 
one or more of these agencies. Since any organ is only a collec- 
tion of cells and their modifications, any change (variation in 
activity, nutrition, etc.) in that organ can be caused only by 
an influence brought to bear on (i) the cells themselves of the 



Xiv INTRODUCTION. 

organ, (2) the blood supply, or (3) the nerve supply; and these 
three factors may be said to so react upon each other that a change 
in one affects both the others. These are the three factors of 
physiological and pathological activity. 



CONTENTS. 



Introduction 



CHAPTER I. 
The Chemical Composition of the Human Body 



CHAPTER II. 
The Cell and the Elementary Tissues 
The Cell . 

The Elementary Tissues 
Epithelial Tissue 
Connective Tissue 
Muscular Tissue 
Nervous Tissue . 
Physiological Characteristics of Striated Muscle 



CHAPTER III. 



Secretion 

Salivary Glands . 
Gastric Glands . 
Intestinal Glands 
Pancreas . 
Liver 

Sebaceous Glands 
Mammary Glands 
Thyroid Gland . 
Adrenal Glands 
Pituitary Body . 
Testis and Ovary 



CHAPTER IV. 
Foods, Digestion and Absorption 
Foods . 

xv 



i7 



27 
27 
31 
3i 

35 
42 

45 

45 



52 

55 
60 

65 
66 
69 
80 
81 
82 
83 
84 
84 



85 
85 



XVI 



CONTENTS. 




Digestion ........ 


89 


Prehension ....... 


92 


Mastication ...... 


92 


Insalivation ...... 


93 


Deglutition ...... 


95 


Gastric Digestion ..... 


98 


Intestinal Digestion ..... 


109 


Large Intestine ...... 


117 


Absorption . . ... 


122 



CHAPTER V 
The Circulation . 

Mechanism of Circulation . 
The Heart . 
The Arterial Circulation 
The Capillary Circulation 
The Venous Circulation 
The Blood 
The Lymph 



131 
132 
132 

*57 

169 

173 
179 
189 



CHAPTER VI. 

Respiration 

Anatomy of the Respiratory Organs . 
Mechanism of Respiration 



195 
197 
203 



CHAPTER VII. 

Excretion 235 

By the Kidneys 235 

By the Skin 251 

CHAPTER VIII. 

Nutrition, Dietetics and Animal Heat . . . 257 

Nutrition 257 

Dietetics 267 

Animal Heat .,,,«... 270 



CONTENTS. 






XVll 


CHAPTER IX. 




The Nervous System 


278 


The Cerebro-Spinal System 






304 


The Spinal Cord 






305 


The Encephalon 






319 


The Medulla Oblongata 






3i9 


The Pons Varolii . 






323 


The Crura Cerebri, Corpora Striata, Optic 


Thalami, Internal Capsule and Corpora 


Quadrigemini ..... 


324 


The Cerebrum 








328 


The Cerebellum . 








342 


The Cranial Nerves 








344 


The Spinal Nerves 








364 


The Sympathetic System 








366 


CHAPTER X. 




The Senses 


373 


Common Sensations . 








373 


Special Sensations 








374 


The Sense of Touch . 








374 


The Sense of Smell 








375 


The Sense of Sight 








376 


The Sense of Taste 








385 


The Sense of Hearing 








386 


The Production of the Voice 








393 


CHAPTER XI. 




Reproduction 








396 



CHAPTER I. 

THE CHEMICAL COMPOSITION OF THE HU- 
MAN BODY. 



The human body contains some fifteen of the chemical ele- 
ments. They are oxygen, carbon, hydrogen, nitrogen, cal- 
cium, phosphorus, sulphur, sodium, chlorine, iron, iodine, 
potassium, magnesium, silicon, flourine ; to these may be added 
accidental traces of lead, copper and aluminium. 

These elements do not appear free in the organism, but unite 
to form various chemical combinations which are termed proxi- 
mate principles. The only exceptions to this statement are fur- 
nished by the uncombined occurrence of oxygen, nitrogen and 
hydrogen in the alimentary canal and of oxygen and nitrogen in 
the blood. These gases in the alimentary canal can scarcely be 
designated as parts of the organism ; while in the blood their 
presence as free gases is comparatively insignificant. Any chem- 
ical element composing a part of the body may, therefore, 
be looked upon as being in combination with one or more of 
the other elements peculiar to animal tissue. The list given 
represents the order in which these elements belong as regards 
their relative quantities in the system. Oxygen constitutes 
more than 70% of the body weight, and carbon, nitrogen, hy- 
drogen and oxygen make up the main bulk of the whole body. 

Organic and Inorganic Bodies. — Certain of these chemical 
combinations cannot be made in the laboratory. When it was 
originally thought that none of the more complex compounds, 
such as urea, sugars, fats, etc. , could be artificially produced, a 
classification of all the chemical compounds existing in bodies 
2 17 



1 8 CHEMICAL COMPOSITION OF THE HUMAN BODY. 

which evidenced phenomena of life was made into inorganic 
and organic, the inorganic being of definite chemical composi- 
tion and possessed of no power to reproduce themselves. Since 
that classification was made the formulae for very many of the 
so-called organic compounds have been determined, and it is 
no longer of any scientific significance, though still adhered 
to. Organic chemistry at present may be defined as the chem- 
istry of the carbon compounds, and organic substances as the 
union of some compound of carbon with some other element or 
elements; they all contain carbon and hydrogen, if carbon diox- 
ide be excepted. At least some of these possess the power of 
reproduction under proper circumstances, and it is these which are 
directly and imperatively necessary to life- — /. <?., to the life of 
protoplasm. 

Many organic substances are also distinguished for the complex- 
ity and instability of their molecules. A very large number of 
atoms of one element and very large number of elements may 
enter into the molecular formula. Those containing a large 
number of elements always contain nitrogen. Now nitrogen is 
exceedingly indifferent in its affinities, and this fact, together 
with the large number of atoms present in the molecule, ac- 
counts for the molecular instability. 

It will be seen that the essential part of the cell is the pro- 
toplasm, and it is essentially the chemistry of protoplasm which 
is under consideration when the chemistry of animal life is be- 
ing discussed. 

Proximate Principles. — The whole body — all the cells of 
which it is composed — is made up of proximate principles, i. e. , 
of various simple and complex substances which represent the 
union of two or more of the 15 chemical elements peculiar 
to the body. The elements combine under chemical laws to 
form proximate principles ; the proximate principles unite to 
form cells ; the cells collectively constitute the body. All prox- 
imate principles are chemical compounds, but not all chemical 



PROXIMATE PRINCIPLES. I 9 

compounds are proximate principles. Not even are all the 
chemical combinations which can be made from the 15 ele- 
ments mentioned proximate principles — simply because all the 
possible combinations do not exist in the body. A proximate 
principle is a chemical compound existing as a part of the body. 
About one hundred are found in the human organism. 

Obviously the first great subdivision of these substances is 
into inorganic and organic ; but they may be further classified as 
(I.) Binary, or Inorganic, (II.) Ternary or Organic Non-ni- 
trogenized and (III.) Quaternary, Organic Nitrogenized, Pro- 
teid, or Albuminoid. 

I. The Binary Proximate Principles are so called because 
they contain two elements, as H 2 0, NaCl, etc. In such sub- 
stances as H 2 S0 4 , etc., the radical, under the definition, must be 
considered as one element. 

As a rule, binary principles pass through the system unaltered ; 
they leave it, by whatever route, without being changed into 
other substances. They may be regarded as already digested, 
and their composition as unaffected in the alimentary canal or 
elsewhere. This is a statement, however, which cannot be ap- 
plied literally to sodium chloride and a few other substances. 
Some sodium chloride is decomposed to form hydrochloric acid 
of the gastric juice, but this is not saying that it is discharged 
from the body as hydrochloric acid or that it may not be dis- 
charged as sodium chloride finally. Some other like exceptions 
also occur, but the number is insufficient to invalidate the gen- 
eral application of the rule. 

Some inorganic materials are also newly formed in the body. 
More water, e. g. , is discharged than is ingested and the same is 
true of sulphates, carbonates and phosphates. The explanation 
is that such substances result from the decomposition of organic 
materials. 

The binary proximate principles are furnished by the ordinary 
foods and drinks. It is not to be understood that they are 



20 CHEMICAL COMPOSITION OF THE HUMAN BODY. 

always taken into the system as so many simple free binary com- 
pounds ; they frequently form necessary parts of organic sub- 
stances and cannot be separated without destruction of the 
identity of those substances. In such cases they are deposited 
in the tissues with the organic substance and when that matter 
has served its purpose and is ready to be discharged as effete 
material they are discharged with it. Much inorganic material 
is necessary to life, though in ordinary meals a surplus is usually 
consumed. 

Water. — The most important of the binary proximate prin- 
ciples is water. It is present in every tissue of the body and 
constitutes more than two-thirds the body weight. Not only is 
it taken in with ordinary food and drink, but it is formed in 
the body in the process of organic disassimilation. Distilled 
water is colorless, odorless, and tasteless, but ordinary drinking 
water may be said to have an agreeable taste by reason of dis- 
. solved salts and air. It is being continually discharged from 
the body and its frequent ingestion is necessary to preserve a 
balance. It is the universal solvent, constitutes the bulk of all 
the fluids of the organism, and is the vehicle of all interchange, 
osmotic or otherwise, in the body. In order to get an idea of 
its function and importance it is sufficient to conceive of its 
withdrawal from the tissues. They lose their physical properties, 
becoming hard and brittle instead of soft and flexible. The ab- 
straction of five or six per cent, of the water from the body, as 
in cholera, causes a viscid condition of the circulating fluids and 
subsequent violent convulsions. By its evaporation from the 
surface it is of very great value in regulating the body tem- 
perature. 

Sodium Salts. — Sodium chloride can scarcely be said to be of 
inferior importance to water. It is ingested with the ordinary 
foods, but usually they do not contain enough of this salt to 
satisfy the demands of the system and it is added as a condi- 
ment to articles of diet. Its withdrawal from the blood is fol- 



BINARY PROXIMATE PRINCIPLES. 2 1 

lowed by grave errors of nutrition and finally probably by death. 
Taken with the ordinary meals it adds flavor to the food and pro- 
motes the flow of the various secretions. It is found in all the 
fluids and tissues of the body except the enamel of the teeth. 

Its particular office is to facilitate and govern osmotic action. 
It will be seen that this office is accomplished mainly, so far 
as the salts are concerned, by considerations of density, the 
less dense fluid passing through animal membranes with greater 
facility than the more dense. Hence the reason for preferably 
giving magnesium sulphate in concentrated solution, since its 
action is dependent upon the establishment of an osmotic cur- 
rent away from the blood. Oysters planted at the mouth of 
fresh-water streams appear fatter because more fresh than salt 
water is taken up by them. This action of sodium chloride is 
especially noticeable in connection with the red corpuscles, 
which swell up on addition of pure water to the blood, but 
shrivel when the amount of sodium chloride is raised above the 
normal. Consequently it is found that the proportion of this 
salt in the plasma is fairly constant, so much so that a watery 
solution of sodium chloride of the same concentration as plasma 
— .65 per cent. — is known universally as the "normal salt so- 
lution" and is the proper strength to inject directly or indi- 
rectly into the circulation. Sodium chloride belongs especially 
to the fluids of the body. It is not deposited in large quantity 
in the tissues, but seems to regulate the appropriation of other 
matters. During gastric digestion the cells of the stomach form 
hydrochloric acid out of the sodium chloride in the circulating 
blood. At that time the discharge of this salt through the urine 
is diminished. It is a constituent of all the excreta. 

Sodium sulphate, phosphate, carbonate and bicarbonate are also 
present in some of the body tissues and fluids. The fluids like 
blood, lymph, etc., owe their alkaline reaction chiefly to sodium 
carbonate. Since an acid coagulates protoplasm and since 
acidified media will not take up carbon dioxide from the tissues 



2 2 CHEMICAL COMPOSITION OF THE HUMAN BODY. 

the importance of the alkaline reaction of the tissues and blood 
is apparent. Sodium carbonate is not introduced in the food 
but is formed by chemical decomposition in the body. 

Potassium Sails. — These may be said to belong to the solids. 
For instance, potassium salts are present in the red corpuscles 
to the almost complete exclusion of sodium salts, while in the 
plasma an opposite condition prevails. 

Acid potassium phosphate is responsible for the acid reaction 
of the muscles in rigor mortis. The potassium salts are analo- 
gous in their general uses to the sodium salts. Some of them are 
formed in the circulating blood. 

Calcium Salts. — Calcium is the most abundant of the metal- 
lic elements in the body. It is always accompanied by mag- 
nesium. Calcium chloride, fluoride, sulphate, phosphate and 
carbonate are all found in various fluids and solids of the body, 
but chiefly in bone. 

The phosphate is abundant in ordinary food and forms the 
chief mineral constituent of osseous tissue. Withdrawal of it 
from the food occasions serious nutritive disturbances, particu- 
larly in the bones. It is responsible for the hard texture neces- 
sary to proper functional activity of this tissue. It is most 
abundant in the bones of the lower extremities which have to 
support the body, while the proportion in the ribs is much less. 
It is largely the absence of this salt which accounts for the mis- 
shapen bones of rachitic individuals. 

Iron. — This element is found essentially in hemoglobin of 
the blood. Its amount is small but none the less necessary. 
Simple anemia is due to a lack of iron in the red corpuscles and 
usually prompt relief follows its administration. The quantity 
existing in ordinary food is commonly sufficient for the needs of 
the organism. Peroxide and phosphate of iron are also found in 
various parts of the body, but hemoglobin contains the neces- 
sary part of this element. The iron is in the hematin part of 
the hemoglobin molecule. 



TERNARY PROXIMATE PRINCIPLES. 23 

The above are only a few of the more important binary proxi- 
mate principles. The behavior of all is subject to the same 
general laws. They cannot be built up into organic material, 
and consequently cannot of themselves sustain life since proto- 
plasm is life, and protoplasm is organic. 

II. The Ternary Proximate Principles are so called because 
they contain three and (excepting phosphorized fat) only three 
chemical elements — carbon, hydrogen and oxygen. These sub- 
stances are of animal and vegetable origin and definite chemical 
composition. They are divided into (A) Carbohydrates includ- 
ing (1) starches and (2) sugars, and (B) Hydrocarbons includ- 
ing (1) neutral fats and (2) fatty acids. 

(A) Carbohydrates were originally defined as bodies contain- 
ing carbon, hydrogen and oxygen, in the molecules of which 
bodies the number of carbon atoms is 6 or some multiple thereof, 
while the hydrogen and oxygen exist in the proportion to form 
water. From a chemical standpoint this definition is not now 
strictly true, but may be accepted as practically correct for pres- 
ent uses. 

1. Starch (C 6 H 10 O 5 ) exists in nearly all plants, and particu- 
larly in the seeds of cereals such as rye, wheat, barley, rice, corn, 
etc., in various roots, as potatoes, and in many fruits. The 
starch granule consists of an envelope of cellulose and the con- 
tained substance, granulose. It is a prominent article of food. 
It is of no value as such but is changed into dextrose (C 6 H 12 6 ). 

2. The sugars are of various kinds when taken into the ali- 
mentary canal, but are changed to dextrose before assimilation. 
Cane sugar (saccharose), milk sugar (lactose) and grape sugar 
(dextrose, glucose) are the most important taken as food. Be- 
sides milk sugar the animal kingdom furnishes liver sugar 
(glycogen) and muscle sugar (inosite). A number of other 
sugars may also enter the alimentary canal, as dextrin, levulose, 
galactose, etc. Some of these represent products in the hydro - 
lytic process which results in the final conversion of all sugars 



24 CHEMICAL COMPOSITION OF THE HUMAN BODY. 

into dextrose. This is probably the only kind of sugar that can 
be found in the blood or other fluids in the body except lactose 
in the milk. Although sugar may be stored up in the liver and 
muscles as glycogen and inosite, dextrose is to be regarded as 
the sugar of the organism. It is to be noted that practically 
speaking this is the form assumed previous to absorption by all 
the carbohydrates, both starches and sugars. The carbohydrates 
are all crystallizable. 

(B) Hydrocarbons contain the same elements as carbohy- 
drates, but in more variable proportions. They are relatively 
poor in oxygen. They are contributed by both animal and 
vegetable kingdoms. They are found in well nigh all animal 
tissues and in nuts, seeds, grains, etc. 

i. The neutral fats are olein, palmitin and stearin. All 
animal fat is a mixture of these three. 

Olein is liquid ; the others are solids. They represent the 
union of fatty acids with glycerine. The application of heat in 
the presence of alkalies will decompose them into glycerine and 
fatty acids, the latter not remaining as acids, but uniting with the 
alkali bases to form soaps. The neutral fats are soluble in chlo- 
roform, ether, and hot alcohol. 

2. The fatty acids are oleic, palmitic and stearic, but since an 
acid as such cannot be allowed in the organism they exist as 
the oleates, palmitates and stearates of the various alkali bases. 
In contradistinction to the neutral fats they are always com- 
bined. 

The general function of all the ternary proximate principles 
is to furnish energy for the running of the body machine. They 
are fuel for the engine. They are insufficient for the mainte- 
nance of life because they contain no nitrogen, and protoplasm is 
nitrogenous. 

III. The Quaternary Proximate Principles are so called 
because they contain four or more chemical elements. They 
always contain carbon, hydrogen, nitrogen and oxygen, and 



QUATERNARY PROXIMATE PRINCIPLES. 25 

usually .sulphur and phosphorus. They may in addition contain 
any of the remaining elements found in the body. 

This class cannot be discussed with satisfaction and accuracy 
from a chemical standpoint because their composition is indefi- 
nite. The provisional formula C 72 H 112 22 N 18 S may be accepted 
for albumin which belongs to this class. They are also called 
nitrogenized, or proteid, or albuminoid proximate principles. 
They are derived from both animal and vegetable kingdoms and 
are not crystallizable. They do not pass through the organism 
unchanged and must be converted into crystalloids before they can 
be absorbed from the alimentary canal. The chief articles of 
diet containing these substances are lean meats, eggs, milk, legu- 
minous vegetables, cereals, etc. 

It is this class of proximate principles which under proper 
conditions manifest the phenomena of life. They are mainly 
concerned in the structure of the solid tissues of the body and 
are also present in all the fluids. They give to any tissue an 
individuality which differentiates its function from that of other 
tissues. They are immediately necessary to the life of proto- 
plasm and consequently to the continuance of functional activity. 
Their withdrawal tells directly upon the protoplasm itself. 

A characteristic of these bodies is that when suitable con- 
ditions of heat and moisture are present they undergo putrefac- 
tion. Another is that they are coagulated at a temperature of 
130 F. or over and by acids. Hence the necessity of a well- 
regulated heat balance and the perservation of an alkaline reac- 
tion throughout the organism generally. In the stomach and 
intestinal tract they are converted into peptones which being os- 
motic are carried away by the blood (though not as peptones) 
to be appropriated in large part by the living proteid tissues for 
their regeneration. Quaternary proximate principles at last 
undergo decomposition in the body with the final production of 
urea, carbon dioxide, water and heat. They are the most impor- 
tant of the three classes. 



26 CHEMICAL COMPOSITION OF THE HUMAN BODY. 

The nitrogenous proximate principles embrace the proteids 
and the albuminoids, both of which are similar in composition. 
Some of the best known of these are albumin of eggs, myosin of 
muscle, casein of milk, paraglobulin, fibrinogen and serum al- 
bumin of blood, pepsin of gastric juice, gelatin, mucin, chon- 
drin, fibrin, etc. 



CHAPTER II. 
THE CELL AND THE ELEMENTARY TISSUES. 



(A) THE CELL. 

All the tissues of the body are made up of cells and intercel- 
lular substance. All the cells are descended from one parent 
cell, called the ovum, while the intercellular substance is cre- 
ated through the medium of the cells. 

Fig. i. 



Nuclear membrane 



Nuclear fluid 
(matrix). 



Nucleolus. 



Chromatin cords 
(nuclear network). 



Nodal enlarge- 
ments of the 
chromatin. 




Cell membrane. 
Exoplasm. 

Microsomes. 
Centrosome. 

Spongioplasm 
Hyaloplasm. 



r-^r— Foreign inclosures. 



Diagram of a cell. 
Microsomes and spongioplasm are only partly drawn. {Brubaker.) 

A cell may be defined as an irregularly round or oval mass of 
protoplasm of microsopic size, enclosing usually a small indis- 

27 



2 8 THE CELL AND THE ELEMENTARY TISSUES. 

tinct spherical body, the nucleus. While these are the typical 
cell elements, cells often possess a thin wall, or surrounding 
membrane, and the nucleus may contain one or more smaller 
bodies, called nucleoli. 

The greater part of the cell contents is protoplasm. This is 
a gelatinous or semi-fluid, granular substance, transparent, and 
generally colorless. It is not a homogeneous mass, but is com- 
posed of an elastic network, called the spongioplasm, enclosing 
a less firm portion, the hyaloplasm. Chemically protoplasm 
consists of various albuminous substances, and a special nitrog- 
enous proteid, plastin, together with water and salts. 

The part played by the nucleus in the reproduction of the 
cell gives it great importance. It is a specialization of proto- 
plasm, traversed by a network of fibrils, enclosing a probably 
semi-fluid portion, the matrix. The name chromatin is often 
given to the fibrils, from their affinity for certain stains, while 
the matrix, which does not take these stains, is termed achromatin. 
The nucleus has a limiting wall or membrane, and often con- 
tains one or more smaller bodies, nucleoli, concerning which 
but little is known. A small body, the centrosome, lies usually 
just outside the nucleus. It is most prominent when cells are 
dividing or about to divide, and has been supposed to give the 
primary impulse to karyokinesis, but this is not certain. It has 
an attractive influence on the protoplasmic fibrils in the neigh- 
borhood producing the "attraction sphere" (see Fig. i). 

Nuclei are especially distinguished : (a) By their resisting 
the power of certain acids and alkalies (e. g., acetic acid), by 
which they are rendered more clearly visible under the micro- 
scope. This indicates some chemical difference between the 
protoplasm of cells and that of nuclei, since the former is de- 
stroyed and rendered invisible by these reagents. (^) By 
staining in hematoxylin, carmine, etc. 

Nuclei are round or oval, and may occupy any position in 
the cell. They are more constant in size and shape than the 



PROPERTIES OF CELLS. 29 

cell itself, but sometimes may occupy nearly the whole of that 
body. 

Properties of Cells. — The properties of cells in general are 
(1) motion, (2) irritability, (3) nutrition, (4) growth and (5) 
reproduction. 

1. Motion. — This manifestation is well illustrated in its lowest 
' form by a fresh-water organism, the ameba, the movement of 

which is called ameboid. In this, the cell, which has hitherto 
remained smooth in outline, throws out little projections from 
its body, like limbs, into which the protoplasm gradually 
streams, thus radically changing the shape of the cell, and 
finally its position. Higher degrees of motion are seen in the 
contraction of muscle cells and the waving of cilia. 

2. Irritability. — The ameboid movement of cells is spon- 
taneous, but motion may also be excited by external influences, 
viz., thermal, mechanical, nervous, chemical and electrical. 

3. Nutrition includes the wonderful processes of anabolism 
and katabolism, by which cells take in certain foods and so 
change them as to nourish and build up their tissue, and throw 
out the parts which cannot be used. 

4. Groiuth follows as a natural sequence of proper nutrition, 
and may cause a uniformly increased element ; but in higher 
organisms growth is usually unequal, to which phenomenon the 
specialization of cells is due. Thus cells assume special forms 
or special functions : some become nerve, others bone, some 
develop the power to contract, others to secrete, etc. 

5. Reproduction. — By this property cells are enabled to repro- 
duce themselves. There are two methods, by (a) direct and 
(b ) indirect division. In the first the cell divides into two by 
the simplest method possible, the nucleus and cell protoplasm 
constricting in the center until two cells are formed. This is 
an unimportant method in the higher animal life we are study- 
ing. The chief manner of reproduction in animal cells is by 
indirect division, known as karyokinesis or mitosis. 



3° 



THE CELL AND THE ELEMENTARY TISSUES. 



In the beginning of this phenomenon, the nucleus, which 
plays the important role, grows larger. Its chromatin greatly 
increases and becomes contorted so as to form a dense convolu- 
tion, the close skein, or spirem. Then the chromatin fibrils 
further thicken, but become less convoluted, forming irregularly 
arranged loops, the loose skein. During the formation of these 



Close Skein 

(viewed from the 

side); Polar field 



FIG. 2. 

Loose Skein 
(viewed from above- 
pole). 



from the 



Mother stars 
(viewed from 
the side). 




Mother Star Daughter Star 

(viewed from above). 



Beginning. 



Division of the Protoplasm. 
Karyokinetic Figures Observed in the Epithelium of the Oral Cavity of a 

Salamander. 

The picture in the upper right-hand corner is from a section through a dividing egg of Sire- 
don pisciformis. Neither the centrosomes nor the first stages of the development of the spin- 
dle can be seen by this magnification. X 560. (From Brubaker.) 

skeins the nuclear membrane and the nucleoli disappear. The 
fibrils of the loose skein now separate at their peripheral turn i 
into a score of loops, the closed ends of which point toward a 
common center — a clear space called the polar field. Seen 
from above these loops of chromatin make a wreath called the 
mother wreath ; seen from the side, they make a star, called the 



EPITHELIAL TISSUE. 3 I 

mother star ox aster. While the loose skeins are forming, deli- 
cate striae appear within the achromatin, so disposed as to make 
two cones with their bases within the polar field and directed to- 
ward one another, and their apices directed toward the future 
new nuclei. These achromatin figures constitute the nuclear spin- 
dle. They then arrange themselves into two daughter wreaths, 
or asters, similar to the mother. At tnis juncture the cell pro- 
toplasm begins to divide by becoming constricted in the center. 
The daughter stars are converted into two new nuclei, in inverse 
order as the original nucleus was broken up. First the loose 
skein forms, then close skein. Nuclear membranes and nucleoli 
appear, the cell protoplasm divides into two new cells, and the 
cycle is completed. (See Fig. 2.) 

Derivation of Tissues. — The primary parent cell divides into 
an innumerable mass of cells, which is called the blastoderm. 
The blastoderm soon divides into two more or less distinct layers, 
an outer and inner, named ectoderm and entoderm, between which 
a middle layer later appears, the mesoderm. 

All the tissues of the body develop, by specialization, from 
these three. (See Embryology.) 

(B) THE ELEMENTARY TISSUES. 

Four varieties of elementary tissues are usually named, ( 1 ) 
epithelial, (2) connective, (3) muscular and (4) nervous. 

1. The Epithelial Tissues. 

Epithelium is a tissue consisting of one or more layers of cells, 
covering all the free surfaces of the body. That covering the 
skin and mucous membranes is ( 1 ) epithelium proper, while that 
covering the serous membranes is known as (2) endothelium. 

1. Mucous membranes secrete a tenacious fluid known as 
mucus, and furnish a lining surface for all tracts with external 
openings, i. e. y the digestive, respiratory and genito-urinary 
tracts. 



32 THE CELL AND THE ELEMENTARY TISSUES. 

2. Serous membranes secrete a watery fluid which acts as a 
lubricant for the walls of closed sacs to move smoothly against 
one another. They line those surfaces without direct external 
openings, such as the pleura, pericardium, peritoneum, heart and 
blood-vessels, synovial surfaces of joints, lymphatic spaces and 
vessels, etc. 

Epithelial tissue performs various functions in different parts 
of the body. In the skin, where it is known as epidermis, it 
protects the delicate surface of the true skin beneath ; in the 
alimentary and genito-urinary canals it aids in secretion and 
excretion; in the respiratory tract it preserves an equable tem- 
perature by the moisture it produces, while in all internal parts 
it yields lubricants. 

Epithelial cells are connected together by an interstitial 
cement substance. They contain no blood-vessels and no 
nerves, being nourished by absorption through clefts of this sub- 
stance. The tissue usually rests upon a basement membrane, or 
membrana propria, which is a modification of the connective 
tissue beneath. 

Varieties. — The varieties of epithelium may be classed as 
follows : (I) Squamous, (a) simple, consisting of a single layer, 
(b) stratified, consisting of several layers ; (II) Columnar, (<?) 
simple, {I?) stratified ; (III) Modified, (a) cilitated, (b) goblet, 
(0 pigmented, (d) glandular, (<?) neui r o-epitheliu7?i. 

I. Squamous Epithelium. — (a) As a simple layer this occurs 
in but few places, lining the air sacs of the lungs, the mastoid 
cells, membranous labyrinth, and crystalline lens. Viewed from 
above, it appears as flattened, polyhedral nucleated plates like a 
regular mosaic. 

(b) Stratified squamous epithelium is far more common. 
This we find covering the true skin, the cornea, mouth, lower part 
of the pharynx, esophagus, epiglottis and upper part of the 
larynx, and all the urethra in both sexes except the membranous 
and penile portion in the male. 



EPITHELIAL TISSUE. 



33 



The arrangement of the cells is typified in the epidermis. 
The lowest layer of this variety, resting upon the membrana 
propria, is almost columnar in type. As they approach nearer 
the surface, the layers become flatter and more scale-like, and 

Fig. 3. 




Vertical Section of the Stratified Epithelium of the Rabbit's Cornea. 

a, anterior epithelium, showing the different shapes of the cells at various depths from the 
free surface ; b, a portion of the substance of cornea. {Kirkes after Klein.) 

possess less vitality. As the outer layer is worn away, the 
lower, more vigorous layers push upward to the surface to take 
its place. In the middle strata, where the cells are polyhedral in 
shape, we find the so-called prickle cells, which have minute 
projecting spines, by which they are connected with one 
another. 

II. Columnar Epithelium. — This type consists of column or 
rod-shaped cells, set upright, longitudinally striated, and con- 
taining oval -shaped nuclei. 

Ciliated epithelium is more common with this variety than 
with any other. Each of these cells presents, on its free sur- 
face, twenty or more small hair- like, protoplasmic appendages, 
called cilia. During life these small processes are in constant 
rapid motion, waving 'in a direction toward the outlet of the 
cavity in which they are found. In the genital organs they are 
important in bringing together the male and female elements of 
reproduction, while in the respiratory tract they are concerned 
3 



34 



THE CELL AND THE ELEMENTARY TISSUES. 



in aiding the passage of the mucus and in the expulsion of for- 
eign bodies. 

i. Simple columnar epithelium occurs in the alimentary tract 
from the stomach to the anus, mammary glands, seminal vesi- 

Fig. 4. 




Ciliated Epithelium of the Human Trachea. 
a, layer of longitudinally arranged elastic fibers; b, basement membrane; c, deepest cells, 
circular in form ; d, intermediate elongated cells ; e, outermost layer of cells fully developed 
and bearing cilia. X 35^- (Kirkes after Kdlliker.) 

cles and ejaculatory ducts, membranous and penile portions of 
the urethra. 

This variety is found ciliated in the greater part of the uterus, 
and in the brain-ventricles and canal of the spinal cord. 

2. Stratified columnar epithelium occurs in the last part of 
the vas deferens and the olfactory part of the nasal fossae. Cili- 
ated, it occurs in the Eustachian tube, lachrymal ducts, respira- 
tory part of nasal fossae, ventricle of larynx, trachea and bronchi, 
epididymis and first part of vas deferens. 

III. Modified Epithelium. — (a) The ciliated variety has 
been considered. 

(/;) Goblet cells are found on all surfaces covered by columnar 
epithelium, but especially in the large intestine. They secrete 
mucin, the main constituent of mucus, which so distends the 
cell that it ultimately bursts and the mucus is discharged. 




CONNECTIVE TISSUE. 35 

(V) Foreign matters, such as fat, proteid, etc., often invade 
the protoplasm of epithelial cells. When these matters are col- 
ored, the epithelium becomes pigmented. Such cells are con- 
stant in the deeper layer of the 
epidermis, especially of certain FlG - 5- 

races, and in the choroid coat of 
the eye. 

(//) Glandular epithelium may 
be columnar, spherical or poly- 
hedral in shape. It is found 
lining the terminal recesses of 

Secreting glands. The prOtO- Epithelial Cells. 

plasm Of the Cell USUally Contains Some of which are filled with mucus, 

the materials which the gland d > formin g gobiet-iike geiis. (From Yeo 

after Cadiat.) 

secretes. 

(e) The epithelium covering those parts toward which the 
nerves of special sense are directed is epithelium of the high- 
est specialization. It is known as neuro -epithelium y and occurs in 
the retina, the membranous labyrinth and in the olfactory and 
taste cells. 

2. The Connective Tissues. 

These tissues, though developed from the same embryonal 
elements, present varieties differing widely in appearance and 
properties. They all serve the same general purpose in the 
animal economy — that of furnishing a supporting and connect- 
ing framework for the body. Like the other elementary tissues 
they consist of two elements, cells and intercellular substance, 
the latter being far the greater in amount. 

Connective tissue cells are of two kinds, fixed and wandering. 
The former are protoplasmic plates of stellate appearance, with 
a nucleus occupying the thick part of the cell, from which 
branched processes extend. They sometimes are pigmented, as 
in the choroid and iris. Wandering or migratory cells are 
present in many situations. These are larger than the fixed 
variety, and are possessed of typical ameboid movement. 



36 



THE CELL AND THE ELEMENTARY TISSUES. 



The divisions of connective tissue are : I. Fibrous Connective 
Tissue ; II. Cartilage; III. Bone. 

I. Fibrous Connective Tissue. — This variety is subdivided 
into (A) White Fibrous, (B) Yellow Elastic, and (C) Areolar, 
to which three special forms may be added, (a) Mucoid or Ge- 
latinous, (F) Adenoid ox Fetiform, and (V) Adipose. 

(A) White Fibrous Tissue. — This is a true connective tissue, 
and forms ligaments, tendons, and membranes. Examples of 
the last are the muscle fasciae, periosteum, and the investing 
sheaths of glands and nerves. It possesses no elasticity, but 
great strength, and appears as parallel white glistening fibers in 
tendons and ligaments, and as intersecting fibers in membranes, 

Fig. 6. 




Bundles of the White Fibers or Areolar Tissue partly Unravelled. 
{Kirkes after Sharp ey.) 

(B) Yellow Elastic Tissue is characterized by its marked elas- 
ticity, and is found in the vocal cords, longitudinal coat of the 
trachea and bronchi, inner coat of blood-vessels, especially the 
large arteries, and in some ligaments. Its yellow-tinted fibers 



CONNECTIVE TISSUE. 



37 



are seen in parallel waves and are larger than those in the white 
tissue. They sometimes form a web-like layer, as in the fenes- 
trated membrane of Henle in the arteries. 

Fig. 7. 




A Teased Preparation of Connective Tissue, 

Showing fine and coarse elastic fibers mingled with bundles of fibrillar tissue and connec- 
tive tissue corpuscles. ( Yeo. ) 

( C) Areolar Tissue is widely distributed and constitutes the 
connecting layer beneath the skin, submucous and subserous tis- 
sues, and between muscles. It receives its name on account of 
the areolae or spaces within its substance, which admit the adja- 
cent parts to move easily upon one another. It consists of white 
and yellow fibers in about an equal proportion. 

(a) Mucoid or Gelatinous Tissue forms the " jelly of Wharton" 
in the umbilical cord, and is found in other situations in the 
fetus, and in the vitreous humor of the eye in the adult. 

(<£) Adenoid Tissue. — This consists of a very delicate network 
of fibers, and is found in mucous membranes and forming the 
reticulum or framework of the spleen and lymphatic glands. 

(V) Adipose, or Tatty Tissue, exists in nearly all parts of the 
body, except the subcutaneous tissue of the eyelids, the penis 
and scrotum, nymphse, within the cavity of the cranium, and in 
the lungs except near the roots. It is nearly always found within 



3« 



THE CELL AND THE ELEMENTARY TISSUES. 



the meshes of areolar tissue, where it forms lobules of fat. Fatty 
matter, in the form of oily, and not distinct adipose, tissue, is 

Fig. 8. 




Fig. 9. 



c "V c 

Group of Fat-cells (f c) with Capillary Vessels (c). (Kirkes after Noble Smith.) 

found in the brain, liver, blood and chyle. The tissue is densest 
beneath the skin, especially of the abdomen, around the kidneys, 

on the surface of the heart between 
the furrows, and in bone marrow. 
Its blood supply is rich. 

II. Cartilage. — There are three 
forms, (A) Hyaline, or true, (B) 
Yellow elastic and ( C) White 
fibrous. 

(A) Hyaline is the typical va- 
riety. It forms the articular sur- 
faces of bones, the costal cartilages, 
and the larger cartilages of the 
larynx, trachea and bronchi, nose 
and eustachian tube. In the em- 
bryo this cartilage forms nearly the 
whole of the future bony skeleton. 
It is of firm consistence, consider- 




i i 

>-? '-'** 
Section of Hyaline Cartilage 
From the end of a growing bone, 
showing a decrease in the intercellular 
substance compared with the number 
of cell-elements, which are arranged in 
rows. (Yeo.) 



CONNECTIVE TISSUE. 



39 



able elasticity, and pearly blue in color. It is enveloped in a 
fibrous membrane, the perichondrium, from the vessels of which 
it derives its nutrition. Like all cartilage, it is composed of 



Fig. io. 



-if^ 




Elastic Fibro-cartilage, 
Showing cells in capsules and elastic fibers in matrix. (From Yeo after Cadzat.) 

cells imbedded in a matrix. The cells are irregular in outline, 
and arranged in patches of various shapes. 

Fig. ii. 




White Fibro-cartilage, 

Showing cells, a, in capsules and fibrillar matrix, b. ( Yeo after Cadiat.) 

(i>) The yellow elastic type exists in the external ear, epi- 
glottis, cornicula laryngis, and eustachian tube. The matrix is 



4-0 THE CELL AND THE ELEMENTARY TISSUES. 

composed almost entirely of fine fibers very much like the yellow 
variety of elastic tissue. 

( C) In white fibrous cartilage the matrix is made up almost 
entirely of white fibrous tissue. It is found as : ( i ) interar- 
ticalar jibro- cartilage, in the semilunar cartilage of the knee- 
joint ; (2) circumferential, on the edges of the acetabulum and 
glenoid cavity; (3) connecting, between vertebrae; (4) strati- 
form, forming a coating to grooves on bones, through which ten- 
dons glide. 

On boiling, cartilage yields a substance, known as chondrin, 
which on cooling turns to gelatin. 

III. Bone. — Bone is a dense form of connective tissue con- 
stituting the skeleton or framework of the body. It serves to 
protect vital organs in the skull and trunk, and acts as levers in 
the limbs worked by muscles. The tissue is characterized by 
the deposit of calcareous or lime matters within its intercellular 
cement substance, to which its well-known hardness is due. 
We find in bone two distinct kinds, dense or compact, forming 
the outer portion, and spongy or cancellous, forming the inner 
portion. 

Microscopically bone is seen to consist of many minute longi- 
tudinal channels, called Haversian canals, each surrounded by 
concentric layers of bone called lamellae, within which run still 
smaller longitudinal channels, called lacunae. Connecting the 
main canal and the lacunae, and radiating in all directions be- 
tween them, are other very minute channels known as canaliculi. 
Each Haversian canal, with its surrounding lamellae, lacunae 
and canaliculi, composes an Haversian system. (See Fig. 12.) 

Periostewn forms the membranous covering of the outer sur- 
face of all bones except their articular extremities. It consists 
of an outer and an inner layer. The outer is a dense fibrous 
coat protecting the more important internal structure called the 
osteogenelic layer, from its intimate connection with the develop- 
ment of bone. It possesses a rich blood supply which nour- 



CONNECTIVE TISSUE. 



41 



ishes the subjacent bone, and contains numerous cells which 
later become bone -forming elements — the osteoblasts. 

Bone marrow is the highly vascular substance found within the 
central cavity of the long bones and the Haversian canals. 
That of the adult long bone is a yellow in color, and is com- 
posed mainly of fat, while that occupying the spaces of cancel- 
lous tissue is red, profuse in blood supply, and contains but 
little fat. Large, multinucleated cells are found in red marrow, 

Fig. 12. 




Transverse Section of Compact Bony Tissue (of Humerus) 

Three of the Haversian canals are seen, with their concentric rings ; also the lacunae, with 
the canaliculi extending from them across the direction of the lamellae. The Haversian aper- 
tures were filled with air and debris in grinding down the section, and therefore appear black 
in the figure, which represents the object as viewed with transmitted light. The Haversian 
systems are so closely packed in this section that scarcely any interstitial lamellae are visi- 
ble. X I 5o- {Kirkes after SharJ>ey.) 

and are known as giant cells, or osteoclasts. They are sup- 
posed to be concerned in the absorption of bone tissue. 

Development of Bone. — According to its development from 



42 



THE CELL AND THE ELEMENTARY TISSUES. 



Fig. 13. 




Two Fibers of Striated 
Muscle, 

In which the contractile sub- 
stance, m, has been ruptured 
and separated from the sarco- 
lemma, a and j ; p, space under 
sarcolemma. (From Yeo after 
Ranvier.) 



the embryo, bone may be classed as : (a) 
Endochondral, derived from the primary 
cartilage, hyaline in type ; (F) Periosteal, 
derived from the primary peripheral per- 
iosteum. All the bones belong to the 
former group, except those of the vault 
of the cranium (parietal and frontal) and 
of the face and a part of the lower jaw. 

The process of bone formation is a 
complicated one. The osteoblasts are 
the main agents, whether the bone be 
derived from cartilage or from perios- 
teum. These cells arrange themselves in 
different locations, the so-called centers 
of ossification, over the surfaces of the 
cartilaginous network or periosteal fibers, 
as the case may be, and soon are trans- 
formed into bone-cells, embedded in a 
matrix, which is at first soft and finally 
becomes ossified from the deposit of lime 
salts. 

3. The Muscular Tissues. 

There are two variations of muscular 
tissues : (A) Striated or Voluntary, and 
(i?) Non-striated or Involuntary. The 
muscle of the heart is striated, but in- 
voluntary. 

(A) Striated muscle, or voluntary, so 
called because it is controlled by the will, 
constitutes the extensive muscular system 
of the skeleton, and of the walls of the 
abdomen, besides a few of the muscles 
connected with certain organs, the mid- 



MUSCULAR TISSUE. 



43 



die ear,, tongue, pharynx, larynx, dia- 
phragm, generative organs, etc. 

This variety of muscle is composed of 
bundles of fibers, called fasciculi, each 
enclosed in a net-like sheath, \hz perimy- 
sium. Between the fibers is a delicate 
cementing substance, the endomysium. 
A layer of areolar tissue, of variable thick- 
ness, known as the epimysium, surrounds 
the entire muscle. 

Each fiber consists of the sarcolemma, 
or investing sheath, the muscle substance, 
and the muscle nuclei. The sarcolemma 
is a tough, homogeneous, elastic mem- 
brane, very tightly adherent to the sub- 
stance of the muscle. The nuclei are 
oval or fusiform, and lie immediately be- 
neath the sarcolemma, upon the surface 
of the muscle substance. 

Seen under the microscope on longi- 
tudinal section voluntary muscle presents 
alternate light and dark transverse striae, 
the explanation of which is a difficult 
problem, for which many solutions have 
been offered. That of Rollett seems 
most plausible. According to this au- 
thor, striated muscle tissue is composed 
of darker contractile fibrillar, arranged in 
parallel rows of delicate spindles, with a 
semi-fluid, lighter portion between, called 
the sarcoplasm. The apposition of the 
spindles transversely produces the so- 
called transverse disks. Each spindle ter- 

, . , , , . differentiation of the protoplasm 

minates in a minute spherical bead, the can be we!1 seen . 




Cells of Smooth Muscle- 
tissue from the Intes- 
tinal Tract of Rab- 
bit. ( From Yeo after 
Ranvier. ) 
A andi?, muscle-cells in which 



44 



THE CELL AND THE ELEMENTARY TISSUES. 



apposition of which transversely produces the intermediate disks, 
or Kranse* s membrane. It is to these alternate dark rows of 
transverse and intermediate disks, with the lighter sarcoplasm 
between, that the striated appearance of voluntary muscle is due. 

The contractile fibrillar are arranged in bundles or muscle 
columns, surrounded by thick layers of sarcoplasm. On the 
cross-section these bundles appear in a network of sarcoplasm as 
minute polyhedral areas, called Cohnheim's areas or fields. 

The blood-vessels of striated muscles are very numerous. The 
larger vessels, together with the nerves, are contained within the 

Fig. 15. 




Striated Muscular Tissue of the Heart, 
Showing the trelliswork formed by the short branching cells, with central nuclei. ( Yeo.) 

perimysium, from which the primitive bundles are supplied by 
smaller branches. The lymphatic supply is scanty. Nerves are 
profusely distributed. 

(j5) Non-striated, or involuntary muscle forms the coats of 
the (1) digestive tract from the middle of the esophagus to the 
anus, (2) capsule and pelvis of the kidney, ureter, bladder and 



PHYSIOLOGY OF STRIATED MUSCLE. 45 

urethra, (3) trachea and bronchi, (4) ducts of glands, (5) gall- 
bladder, (6) vesiculae seminales (7) uterus, (8) blood-vessels 
and lymphatics, (9) iris, ciliary bodies, and eye-lids, (10) hair 
follicles, sweat glands, and skin of the scrotum. 

Non-striated muscle is made up of bundles of flat, spindle- 
shaped, nucleated cells longitudinally disposed. Each cell is 
covered by an elastic sheath, corresponding to the sarcolemma 
of striated muscle. An endomysium unites the cells together, 
while a perimysium surrounds the bundles. 

Heart muscle is striated and involuntary, and is thus distin- 
guished from the usual form of striated muscle: (1) Its fibers 
are united with each other at frequent intervals by short 
branches; (2) the fibers are smaller and the striation is less 
marked; (3) the sarcolemma is absent; (4) the nuclei are 
situated within the substance of the fiber and not upon it. 

4. The Nervous Tissues. 

The primary elements of the great nervous system are, (a) 
the cells, which originate nervous impulses, and (b) the fibers 
which transmit such impulses, the two being connected and sup- 
ported by (<f) the neuroglia and connective tissue framezuork. 

These tissues will be described under the later discussion 
of the nervous system. 

PHYSIOLOGICAL CHARACTERISTICS OF STRIATED 

MUSCLE. 

Striated muscle possesses elasticity, tonicity, a peculiar sensi- 
bility, and contractility or irritability. 

The elasticity of muscle is not so much a property of the 
muscle substance as of the sarcolemma and interstitial fibrous 
tissue. There is of course a certain limit to this power, if ex- 
tended beyond which the muscle fibers become dislocated and 
unfitted for further use. 

Tonicity is the constant insensible tendency to contraction 



46 THE CELL AND THE ELEMENTARY TISSUES. 

possessed by muscle in a normal and healthy state. This is seen 
in surgical operations in which muscles after being divided be- 
come permanently contracted. 

Muscle has a special sensibility which enables it to appreciate 
the force of weight, resistance, immobility and elasticity, and 
the sense of fatigue after long-continued exertion. General 
sensibility, as of pain, is but little developed. 

Contractility is a property possessed by striated and non- 
striated muscle. We see it in the former in flexing a limb, 
raising the eye-brows, etc., and in the latter in the variations 
in calibre of blood-vessels and the contraction of the uterus 
in labor. It is noticeable that a voluntary muscle responds 
so quickly to stimuli that the contraction may be said to 
be practically instantaneous. The subsequent relaxation occurs 
as soon as the stimulus is withdrawn. The contraction and re- 
laxation of involuntary muscle is much more sluggish. It is 
the phenomenon as presented in the striated variety with which 
we are most concerned. 

Muscular contractility results from a stimulus which may be 
transmitted from the brain through the conductors of motor 
impulses, as by an act of volition, or it may be produced re- 
flexly, or artificially. 

Artificially, the stimulus may be applied through the nerve 
supplying the muscle, or to the muscle directly, and may be 
mechanical, thermal, chemical or electrical. Electricity fur- 
nishes the most convenient form of stimulus for experimental 
use, because its force can be accurately regulated. 

Muscular contractility can be studied in the dead organism 
for some time after death, especially in cold-blooded animals. 
The power to contract remains the same so long as the nutrition 
has not been disturbed beyond certain limits. Thus, when the 
power is lacking in muscles of a living organism from paralysis 
and disuse, upon minute examination it is found that chemical 
and physical disintegration has occurred. 



PHYSIOLOGY OF STRIATED MUSCLE. 47 

The principal changes noted in muscle on contraction are in 
electrical and chemical phenomena, elasticity, temperature and 
form. 

I. The electrical changes involve the so-called " currents of 
rest." A galvanometer applied to a muscle removed from the 
body indicates the passage through it of certain electrical cur- 
rents. When the muscle is made to contract the galvanometric 
needle returns to zero (the negative variation) ; when it re- 
laxes the needle again indicates the passage of a current. The 
cause of these currents may be chemical changes due to degen- 
erative processes. 

The effects of galvanic and Faradic currents upon muscular 
contractions are indicated under the nervous system. 

II. The chemical changes are : — 

(#) Muscle tissue, which is normally neutral or slightly alka- 
line in reaction, becomes acid, owing to the formation of 
sarcolactic acid. 

(£) More oxygen is taken up from the blood than when the 
muscle is at rest, proof of which is shown by the facts that 
during active muscular exercise more oxygen enters the body by 
respiration, and the blood leaving active muscles is poorer in 
oxygen. 

(V) More C0 2 is produced in the muscle. The increased 
elimination of this gas is far in excess of the increased consump- 
tion of oxygen. Oxygen is stored up in the same way in the 
muscular substance in the intervals of activity. It is a condi- 
tion to be easily called into use when the metabolism incident 
to contractions begins. 

{d) Glycogen, which is ordinarily stored up in the muscle 
substance, is consumed. 

(e) A peculiar muscle sugar, probably inosite, makes its ap- 
pearance. 

The increased output of C0 2 is in striking contrast to the 
practically undisturbed elimination of urea, except after prolonged 



48 THE CELL AND THE ELEMENTARY TISSUES. 

exercise. An explanation of this discrepancy will be given un- 
der Nutrition. 

III. A muscle is not only elastic but extensible. A passive 
weight suspended from the end of a muscle will elongate it ; 
but when the weight is removed the muscle resumes its original 
length. A contracted muscle is more extensible than one at 
rest. Fresh muscle is perfectly elastic, t\ e., it will regain its 
exact normal shape after contraction, elongation, etc. ; but con- 
tinued activity finally impairs this quality. 

IV. Evolution of heat accompanies muscular contraction. It 
will be seen later that all metabolic activity means the pro- 
duction of force, most of which force assumes the form of heat. 
The increased metabolism in muscle tissue during exercise means 
an increased conversion of potential energy of the proximate 
principles into heat and work. The heat produced represents 
by far the larger part of this potential energy. 

Of the total amount of potential energy converted, the part 
taking the shape of work upon conversion is greater the greater 
the resistance to muscular contraction. It follows that the heat is 
relatively diminished ; though the increased metabolism ren- 
ders it not absolutely so, i. e., the amount of heat actually 
produced is greater the greater the tension. The natural, and 
correct, conclusion on this ground is that when a muscle becomes 
fatigued the amount of potential energy taking the form of heat 
is increased. The heat production of muscular activity is invol- 
untarily made use of when a person shivers in cold weather. 

Given a certain amount of work to do, more heat will be 
evolved if it be done by a few strong contractions than by many 
weak ones. 

V. The changes in form are the most striking of those that 
occur. In contracting a muscle becomes shorter and broader, 
the two alterations compensating each other, so that there is no 
change in bulk. The amount of shortening may vary all the 
way up to about 35% of the original length of the muscle. 



PHYSIOLOGY OF STRIATED MUSCLE. 49 

The fresher and more irritable a muscle is the shorter it will be- 
come in response to a given stimulus. Up to a certain limit the 
stronger the stimulus the greater the shortening. Up to about 
85 ° F. heat increases the amount of shortening. The more 
nearly parallel to the long axis of the muscle the fibers run, the 
greater the shortening in proportion to the length. 

Mechanism of Muscular Contraction. — The application of 
electricity to the nerve supplying a given muscle, by one of the 
various apparatus which have been devised for the purpose, shows 
the mechanism of muscular contraction in a graphic manner. 
Two varieties of phenomena may be produced by such an appa- 
ratus. The stimulus may be applied in the form of a single 
electrical discharge, when it is followed by a single muscular 
contraction ; or a rapid succession of discharges may be applied, 
producing a state of permanent, or so-called tetanic, contrac- 
tion. 

Upon the application of a single electrical discharge to a 
motor nerve connected with fresh muscle, there is a sudden con- 
traction, which is succeeded by a sudden relaxation. Under 
this stimulation, the muscle shortens its length about three 
tenths. In man, the time required for the contraction is esti- 
mated at .03 or .04 of a second, and for the relaxation a period 
a little shorter, with about .004 to .01 of a second for the inter- 
val between stimulation and contraction, called the latent 
period. 

Experiments have shown that when one end of a muscle is 
excited, a contraction occurs at that point and travels along the 
length of the muscle in the form of a wave, the estimated ra- 
pidity of which is thirty-three to forty-three feet per second. 
In the contraction of a muscle it is believed that shortening of 
the fiber takes place wherever a stimulus is received, and that 
this is propagated in the form of a wave, which meets in its 
course another wave starting from a different point of stimula- 
tion. 



50 THE CELL AND THE ELEMENTARY TISSUES. 

A rapid succession of electrical impulses applied to a muscle 
produces a persistent, or tetanic, contraction, which is the kind 
that occurs in the normal physiological action of muscle. The 
power of the contraction is proportionate to the rapidity with 
which the stimuli are received. The number of stimuli received 
by a muscle in a state of powerful contraction is probably about 
twenty per second, which produces the same number of waves 
or vibrations in a muscle. These vibrations make a muscle 
sound, of a pitch corresponding to their rapidity. This can be 
heard in the temporal and masseter muscles by filling the ears 
with wax and causing the muscles to contract. 

Chemical Composition of Muscle. — Water represents about 
seventy-five parts per hundred of muscle tissue. Of the re- 
maining 25 parts 15 are proteid ; glycogen, fat, organic and 
inorganic salts (chiefly potassium) constitute the remainder. 

When fresh muscles are subjected to pressure, there is forced 
out a substance, muscle plasma, which corresponds to the plasma 
of blood. The muscle plasma contains a substance, myosinogen, 
analogous to fibrinogen of blood. Coagulation of the muscle 
plasma produces myosin, which is not unlike fibrin in some re- 
spects. 

Muscle Fatigue. — A muscle will not contract indefinitely. 
When it is being artifically stimulated the individual contrac- 
tions become progressively longer and weaker, until response 
finally ceases. It is said to be fatigued. 

The fatigue results from the consumption of the energy-pro- 
ducing materials at hand, but more particularly from the accu- 
mulation of effete products of muscular metabolism — especially 
of sarcolactic acid. 

The seat of fatigue is not, however, in the muscle itself. 
Nor is it in the supplying motor nerve. It seems that the waste 
products poison the nerve terminals in the end motorial plate, 
so that it acts as a block to the passage of an impulse to the 
muscle. It has also been shown that these same waste products 



PHYSIOLOGY OF STRIATED MUSCLE. 5 I 

carried to the centers inhibit their power to originate efferent 
impulses. 

Rigor Mortis. — This is a general stiffening of the musculature 
subsequent to death. Coagulation of the muscle plasma, with 
the formation of myosin, is the cause of the condition. The 
muscles become (a) shortened and opaque, (^ ) heat is evolved, 
(V) they give off C0 2 , and (W) become acid in reaction 
(Kirkes). The acid reaction is due to the presence not only of 
sarcolactic acid, but of acid phosphates as well. 

Rigor mortis usually begins in the neck, and later extends 
progressively to the muscles of the upper extremities, trunk and 
lower limbs. It disappears in the order of invasion. 

Usually the cause of its disappearance is putrefaction, but in 
some cases it lasts so short a time that fermentative changes 
may be responsible. 



CHAPTER III. 
SECRETION. 



Secretion and Excretion. — Ordinarily the product of glandu- 
lar activity is spoken of as a secretion. On the one hand, glands 
may take from the blood substances which are preformed in that 
fluid, which would accumulate and produce detrimental effects 
if not removed, and which are discharged from the body. On 
the other hand, glands may form out of materials furnished by the 
blood substances which are peculiar to that gland's activity, 
which have an office to perform in the economy, which do not 
accumulate on removal of the gland, and which are not dis- 
charged from the body. The product in the first case is an 
excretion, in the second case a secretion. But when it comes 
to naming an exclusively excretory or an exclusively secretory 
gland, the task is found to be practically impossible. Probably 
the most typical excretion of the body is the urine, yet there 
are in the urine substances, like hippuric acid, etc., which are 
undoubtedly formed by the kidney, and which do not preexist in 
the blood. The succus entericus, e. g. , would seem as typical a 
secretion as it is possible to find, but not infrequently it contains 
urea when the activity of the kidney is impaired, to say nothing, 
under normal conditions, of the water and salts which are taken 
as such from the blood. The liver is notable in its secreto- 
excrementitious action. While the desirability of thus separat- 
ing the glands into secretory and excretory and their products 
into secretions and excretions is granted, the impossibility of 
such a division is apparent. 

It is possible in most cases to apply the distinction to the 

52 



GLANDS. 53 

separate constituents of the product of a particular gland, but 
not to the product as a whole. In view of these facts, attention 
will be given in this chapter to several glands which manifestly 
produce excretions as well as secretions. The action of the 
kidney and sweat glands is so predominantly excretory that they 
are treated separately. In what follows the term < ' secretion ' ' 
cannot always be taken as meaning a true secretion, for it is 
customary and convenient to speak of the ' l secretion of urine, ' ' 
for example. 

Glands. — If we conceive of a single layer of secreting epi- 
thelial cells supported by a thin basement membrane, and then 
this structure invaginated or folded in upon itself, so that the 
two layers of epithelium face each other with a greater or less 
interval between them, with the basement membrane constitut- 
ing the external support for both, we will have in mind the 
essential structure of a gland proper. The invaginated cells are 
the gland cells, and the interval between the two layers of cells 
is the lumen. Whether the invaginated structure sends off from 
itself secondary or tertiary folds similar to the original, or 
whether the lumen of any of these folds is in the shape of a simple 
tube or sac, or both, is immaterial. They may all be considered 
as identical in nature with the original invagination and only 
modifications of its architecture. 

However, these modifications are more or less distinguished by 
names. Those which become complex by numerous branchings 
of the involuted tube are usually termed compound, as opposed 
to a single simple fold ; glands are further classified, as tubu- 
lar, racemose, or tubulo-racemose, according as the termina- 
tion of the lumen has the shape of a tube, or sac, or both. 
Thus a simple or a compound gland may belong to any one of the 
three last-named varieties. The crypts of Lieberkuhn are simple 
tubular glands. The glands of Brunner are usually described as 
compound tubulo-racemose structures. 

In a compound gland that portion which communicates with 



54 SECRETION. 

the surface is called the duct and is supposed not to be con- 
cerned in actual secretion, but simply in carrying the product 
away from the secreting terminal ramifications of the subdivi- 
sions of the involution — which terminations are called acini or 
alveoli. It follows, of course, that a collection of acini may dis- 
charge their secretion into the main duct by a smaller duct — 
that is, that the gland may have various subdivisions of the duct 
proper. 

Furthermore secretions are classified as external when they 
are discharged upon a surface communicating with the external 
air, such as the alimentary canal, or skin, and internal when 
they are discharged upon surfaces not in communication with 
the exterior, such as blood-vessels. Both external and internal 
secretions are liquid or semi-liquid in character, for they must 
contain water as a vehicle for the salts and organic substances 
which are present in all of them and which, in fact, distinguish 
them from one another. 

Glands in general have been divided into serous and mucous 
by Heidenhain, according as the secreted fluid is watery and 
thin, or viscid and stringy from the presence of mucin. This 
division is further warranted by histologic differences in the cells 
concerned in each kind of secretion. The cells in a serous 
gland are small and finely granular, and are in close apposition 
to each other. Those of mucous glands are larger, almost 
square and are definitely separated. Many glands contain both 
kinds of cells, but since their secretion contains mucin, such 
glands are usually spoken of as belonging to the mucous variety. 
It will be seen that the salivary glands illustrate these varieties. 

Gland Secretion. — Underneath the basement membrane of a 
gland (that is, on the side opposite the epithelial cells) ramifies 
an abundant network of blood and lymph capillaries. This an- 
atomical arrangement favors osmotic transudation from the ves- 
sels, especially since the pressure in the vessels is normally 
greater than in the acini and ducts of the gland. Numerous 



SALIVARY GLANDS. 



55 



experiments, however, prove the inadequacy of simple osmosis 
to explain all the processes of glandular secretion, especially 
those connected with the presence of organic constituents ; 
while the undoubted presence of secretory nerves (besides the 
vaso -motor nerves to the vessels) would seem to give a priori 
evidence that the glandular epithelium takes some active part in 
the formation of the secretion. Such an office is granted to 
these cells, but whether it is of a chemical, or a physical, or a 
" vital " character is not evident. 

(A) Salivary Glands. 
The chief salivary glands are three in number on each side of 
the mouth — the parotid, submaxillary and sublingual. Besides 
these, there are, throughout the buccal mucous membrane, a 
number of smaller glands of similar structure contributing to 
the formation of saliva. The parotid gland is situated just be- 
neath and in front of the lobe of the ear ; the submaxillary be- 
neath the inferior maxilla about the center of the base of the 




Cells of the Alveoli of a Serous or Watery Salivary Gland. {Brubaker 

after Yeo.) 
A, after Rest ; B, after a short period of activity ; C, after a prolonged period of 
activity. 

submaxillary triangle, and the sublingual beneath the mucous 
membrane of the mouth, just lateral to the lingual frenum. 

The duct from the parotid, Stenson's duct, runs beneath the 
mucous membrane of the cheek to a point opposite the second 
upper molar tooth, where is its opening into the mouth. The 



56 



SECRETION. 



duct from the submaxillary, Wharton's duct, discharges the secre- 
tion from that gland into the mouth by the side of the frenum 
of the tongue. The secretion from the sublingual reaches the 
mouth by a number of small ducts (Rivinus) which open also 
by the side of the frenum, and sometimes as well by a larger 
duct, Bartholin's, which runs parallel with Wharton's and 
empties near it. 

Histology. — In structure the salivary glands have recently 
been shown to be of the compound tubular variety, the secret- 
ing part being tubular instead of saccular, as was once thought. 
The parotid is a serous gland, the other two are usually said to 
be mucous, though they contain both serous and mucous cells. 

Fig. 17. 




Section of a Mucous Gland. {Brubaker after Lavdowsky.) 
A, in a state of rest ; B, after it has been for some time actively secreting. 

The ducts subdivide into smaller ducts and tubes, until a dis- 
tinct tubule is distributed to every acinus and becomes the 
lumen of that acinus. The whole arrangement resembles the 
branchings of a tree. 

The flow from these glands is greatly increased by mastica- 
tion. From the parotid the flow is much more abundant on 
that side upon which mastication takes place. During activity 
it can be shown that the granules of the serous cells accumulate 



1 



SALIVARY GLANDS. 57 

toward the lumen of the acinus while the outer segment of the 
cells becomes comparatively clear. It is supposed that this is 
an essential step in the production of the organic constituents of 
the secretion — that the granules contain either the ptyalin or the 
substance necessary to its formation. It is also supposed that at 
the same time that ptyalin is being thus produced and dis- 
charged, very active constructive changes are occurring in the 
clear zone of the cells. During activity some at least of the 
mucous cells seem to break down, but it is probable that the 
granules in the cell protoplasm become converted into mucin, 
which, being extruded, seems to destroy the cell itself. 

Composition and Properties of Saliva. — While it is possible 
to draw certain distinctions between the saliva from the different 
glands, these distinctions are comparatively unimportant, so far 
as digestion is concerned ; for the secretions from the three 
pairs of glands become mixed in the mouth, and it is their com- 
bined effect which, in any particular case, is observed. Saliva 
contains in 1,000 parts about 994 of water, the remaining six 
parts being organic and inorganic solids. The organic are 
mucin, albumin and ptyalin. The mucin possesses a physical 
value in deglutition. The ptyalin is a digestive enzyme and 
the most important constituent of the secretion. Were it not for 
the presence of epithelial cells in suspension, saliva would 
be clear and transparent. Its reaction is alkaline, its specific 
gravity is about 1004 to 1008, and the average amount of daily 
secretion is about 2 % pounds. 

The parotid saliva is much more watery and mixes much more 
readily with the food than the submaxillary and sublingual, 
which latter is mucilaginous and rather gives to the bolus a 
glairy coating than becomes incorporated in it. The sublingual 
saliva is thicker and more viscid than the submaxillary. 

Nerve Supply. — The connection of the nervous system with 
salivary secretion deserves particular attention, since the phe- 
nomena presented under its influence are typical, and, if not 



58 SECRETION. 

explanatory of occurrences elsewhere in the body, are at least 
very suggestive. 

Each one of the three glands is supplied with both cerebro- 
spinal and sympathetic fibers. Each one of them has three 
kinds of nerve fibers, secretory, vaso-dilator and vaso-constrictor. 
The secretory and vaso-dilator reach the gland in the cerebro- 
spinal trunks ; the vaso-constrictor in the sympathetic. The 
vaso-constrictors and vaso-dilators are distributed to the walls 
of the blood-vessels, and influence secretion indirectly only by 
increasing or diminishing the amount of blood going to the 
glands. The secretory fibers exert their influence directly upon 
the gland cells. It is claimed also that the secretory fibers are 
divided into sets controlling the production of the organic con- 
stituents and sets controlling the production of water and salts. 

The parotid gland receives its cerebro -spinal fibers through a 
branch of the fifth nerve, but when they are traced backward it 
can be shown that they are in the tympanic branch of the ninth, 
and pass from this branch to the small superficial petrosal nerve 
and thence to the otic ganglion — from which ganglion they 
run to the parotid gland by way of the atmcido -temporal branch 
of the third division of the fifth. The cervical sympathetic also 
sends fibers to this gland. 

The submaxillary and sublingual gland are supplied by the 
same nerves. Their cerebro-spinal fibers leave the brain by 
way of the facial, follow the chorda tympani as far as a short 
distance beyond its junction with the lingual nerve, and then 
leave it to reach the submaxillary ganglion and run thence 
to the submaxillary and sublingual glands. These glands receive 
sympathetic fibers from the superior cervical ganglion. 

Influence of Nerve Supply. — Taking the parotid as an ex- 
ample, it is found that stimulation of its cerebro-spinal fibers 
produces an abundant watery flow of saliva ; the gland becomes 
decidedly redder, pulsation is sometimes apparent, and it is 
evident that the amount of blood is locally increased. When 



SALIVARY GLANDS. 59 

the sympathetic supply of the parotid is stimulated, the secre- 
tion is inhibited or reduced to a minimum, the gland becomes 
pale and the amount of blood in it is evidently diminished. 

Similar corresponding results are occasioned in the submax- 
illary and sublingual glands by stimulation of the chorda tympani 
and the sympathetic fibers. 

It would seem at first, in the light of the vascular changes 
accompanying stimulation of the two supplies to all these 
glands, that the resultant phenomena could be explained en- 
tirely by variations in the amount of blood, and that the nerv- 
ous system influences their secretion only by contraction and 
dilatation of the vessels. However, a number of circumstances, 
which it is unnecessary to relate here, prove that the secretory 
fibers exert an influence directly upon the cells themselves, 
causing them to secrete. The mere distribution of these fibers 
to the gland cells presupposes some such function on their part ; 
and it can actually be shown that the secretion can be increased 
when the blood supply is cut off, or without dilatation of the 
vessels. Such action, however, is of course only temporary, for 
the materials for secretion must be supplied by the blood. The 
exact method of termination of the secretory fibers has not been 
determined. It is probable that they end between and around 
the cells and do not penetrate their substance. 

Section of the chorda tympani causes a continuous flow of 
saliva from the submaxillary and sublingual glands for several 
weeks. This has been termed paralytic secretion, and is sup- 
posed to be due to the fact that the chorda fibers do not them- 
selves run directly to the glands, but are distributed to sym- 
pathetic ganglia (the submaxillary or others in the gland sub- 
stance). Section of the chorda, then, causes degeneration of 
its fibers only as far as these ganglia, and their cells are thought 
to be subject, in some obscure way, to continuous irritation 
during the period for which the paralytic secretion continues. 
Afterward the glands atrophy. The same phenomenon in 



60 SECRETION. 

the parotid would doubtless follow section of its cerebro-spinal 
fibers. 

The secretion of saliva is a reflex act. The normal stimulus 
is food in the mouth. The afferent fibers carrying the im- 
pressions to the center are in the branches of the ninth and 
the lingual division of the fifth. The efferent fibers are those 
already noticed — and they carry two different but associated 
kinds of messages, namely, those to the cells causing them to 
secrete, and those to the vessels, influencing secretion by in- 
creasing (or diminishing) the amount of secretory materials by 
increasing (or diminishing) the amount of blood. 

The center for this reflex is in the medulla oblongata, close to 
the origin of several of the cranial nerves. It is a matter of 
common observation that the salivary flow may be increased by 
the thought, or sight, or smell of food, or by other impressions, 
and inhibited by fear, embarrassment, etc. This may be ex- 
plained by the nearness of the salivary center to the roots of 
origin of nerves conveying these impressions to the brain. 

(B) Gastric Glands. 

Varieties. — In the mucous membrane of the stomach are 
found two kinds of glands. According to their relative posi- 
tion with reference to the two ends of the stomach they are 
called fundic and pyloric. It is to be noted, however, that 
neither of these divisions is confined strictly to that portion of 
the stomach which its name would seem to indicate. Accord- 
ing to their secretion the glands are called acid and peptic. 
The fundic and acid, and the pyloric and peptic are considered 
to be identical. But attention is called to the fact that while 
peptic (pyloric) glands secrete pepsin only, the acid (fundic) 
secrete both acid a?id pepsin. 

Structure. — Some of the gastric glands are simple tubules, while 
others maybe bifurcated, so that two (or more) tubules commu- 
nicate with the surface by a single canal. They may all, however, 



GASTRIC GLANDS. 
Fig. i 8. 



61 




Vertical Section of the Gastric Mucous Membrane. 
g,g, pits on the surface; J>, neck of a fundus-gland opening into a duct, g ; x, parietal, 
and y> chief cells ; a, v, c, artery, vein, capillaries ; d, d, lymphatics, emptying into a large 
trunk, e. {Landois.) 

be classified as belonging to the simple tubular variety. They 
have a deep secreting portion and a superficial non-secreting 
portion. The latter is lined by columnar epithelium, and is the 
duct proper. The former is lined by cuboidal epithelium which 
discharges its secretion into the lumen, this lumen being only a 
continuation of the duct. These cuboidal cells are called peptic 
cells because they produce pepsin, or its forerunner, pepsinogen. 



62 



SECRETION. 



The fundic (acid) glands are found to have lying close to the 
basement membrane a number of large cells at intervals between 
the cuboidal cells and not extending outward to the central 

Fig. 19. 




lumen. They are thought to communicate with the lumen by 
capillary ducts, which may even penetrate their substance. 
They are supposed to secrete hydrochloric acid, and are called 
acid cells from this fact, or parietal cells from their position. 
(See Fig. 18.) 



GASTRIC GLANDS. 63 

Properties and Composition of Gastric Juice. — The secre- 
tion of the glands of the stomach is called gastric juice. It is 
thin, colorless, acid in reaction, and has a specific gravity of 
about 1005 to 1009. Some 973 parts per thousand consist of 
water, the remainder of hydrochloric acid and organic and in- 
organic solids in solution. The chief organic constituents are 
mucin, a proteid, pepsin and rennin. The inorganic solids are 
chiefly the chlorides and phosphates. The amount of gastric 
juice secreted in twenty-four hours is from six to fourteen pounds. 

The characteristic and important constituents are hydrochloric 
acid, pepsin and rennin. The gastric juice strongly resists 
putrefaction. The secretion in the pyloric end is said always to 
be alkaline ; that in the fundic always acid. This is accounted 
for by the distribution of the acid and peptic glands already 
noted. Except during digestion, the mucous membrane has a 
neutral or slightly alkaline reaction. 

Method of Secretion. — When food is ingested gastric move- 
ments very soon begin, carrying the food in this direction or 
that, as described later. At the same time, the gastric mucous 
membrane changes from a pale pink to a congested red, and soon 
drops of gastric juice begin to appear. They run to the de- 
pendent portions of the cavity and become incorporated with 
the alimentary mass. It is believed that if the gastric move- 
ments did not occur, this secretion would be limited for fifteen 
or thirty minutes to a very small area, namely, that with which 
the food is in contact. But it is comparatively general because 
the movements bring practically all parts, at least of the fundic 
mucous membrane, in contact with the food before this time has 
elapsed. The idea is that up to fifteen or thirty minutes after 
the introduction of food, the glands are made to secrete by 
direct mechanical stimulation of the food, and after this time the 
secretion becomes general, whether mechanical irritation become 
general or not. 

It ought to be added, however, that in recent years secretion 



64 SECRETION. 

by mechanical stimulation has been denied, and the denial is 
supported by good evidence. Besides direct proof by experi- 
ments, it is shown that this early secretion occurs without 
mechanical irritation, as when food is chewed and made to pass 
through an esophageal fistula, or even by the sight of food. 
These observers (Pawlow) state that food introduced into the 
stomach through a fistula produces absolutely no flow if the 
animal experimented upon does not know of the introduction. 
Under this view the secretion is a distinct reflex, the impressions 
being carried to the center by afferent nerves distributed to the 
mouth, or by nerves of special sense. 

Whether as a reflex or as a result of mechanical stimulation, 
the fact remains undisputed that the flow begins a few minutes 
after the introduction of food, and lasts until gastric digestion is 
completed. After a time it is supposed that chemical changes 
in the food itself further stimulate the gastric glands, through 
their influence on the secretory nerves. These stimulating 
chemical products are not developed alike from all foods ; and 
the conclusion is warranted that some substances do not undergo 
gastric digestion so readily as others. Ordinary bread and the 
whites of eggs, for example, are said not to develop them. It 
has been further shown that fats, oils, etc., actually develop 
substances which chemically inhibit gastric secretion. There 
appears also to be a kind of chemical regulation of the amount 
and quality of juice, according as much or little, or a varying 
acidity, is needed in the digestion of the substance in ventro. 

Conditions influencing digestion operate mainly by producing 
changes in the quantity or quality of gastric juice, and these 
changes in turn are largely effected through the nervous system. 
Fever, overeating, depressing emotions, strenuous physical or 
mental exercise, etc., decrease the secretion and correspond- 
ingly interfere with digestion. 

Changes During Activity. — Like the salivary cells, the cu- 
boidal peptic cells can be shown to undergo changes during 



INTESTINAL GLANDS. 65 

secretory activity. When at rest they contain abundant gran- 
ules, but during secretion these granules disappear, first from the 
base and later from well-nigh the whole cell. The granules are 
supposed to contain pepsin, or rather pepsinogen, for it is 
thought that pepsin is not formed by the cell directly, but is 
made out of pepsinogen, which is the product of the peptic cells, 
probably under the action of hydrochloric acid. The rennin is 
also supposed to exist in the cells as some preliminary material 
corresponding to pepsinogen. This material may be termed 
ren nin zymogen . 

Changes in the acid cells during activity also occur, but are 
more obscure than those in the peptic cells. The source of 
hydrochloric acid is a decomposition of the neutral chlorides of 
the blood and the union of the chlorine thus liberated with 
hydrogen, but how or why this occurs is not explained by phe- 
nomena so far observed. 

Secretory Nerves. — While it has been impossible to demon- 
strate secretory fibers to the cells of the gastric glands, such 
fibers must exist in the vagus. Section of it (and the sympa- 
thetic), however, does not entirely stop the secretion, but in- 
cidents referred to in a preceding section, such as secretion at 
sight of food, or when food is chewed and not swallowed, cer- 
tamly point to an influence of the central system over secretion. 
Of course the sympathetic fibers to the vessel walls are indirectly 
concerned. 

(C) Intestinal Glands. 

Besides the agminate glands, which are discussed under Di- 
gestion and which are probably not true glandular structures, 
the intestinal glands are those of Brunner and the crypts of 
Lieberkuhn. The former exist in the upper duodenum, and are 
of the compound tubular variety. The latter are set throughout 
the small and large intestines and are of the typical simple tubu- 
lar variety. 

The glands of Brunner resemble the pyloric glands, except 
5 



66 



SECRETION. 



that the number of secondary tubules is- much greater. Their 
secreting cells are similar. The amount of secretion from them 
is necessarily very small. Whether they produce any digestive 
enzyme is not known. The crypts of Lieberkuhn resemble the 
pyloric glands, except that they are shorter, seldom bifurcated, 



Fig 




Drawing of Transverse Section of the Duodenum, 

Showing Brunner's glands, B, opening into Lieberkuhn's follicles, L ; V, villi ; M, muscu- 
lar coats. ( Yeo.) 

and their secreting cells are columnar in shape. They are sup- 
posed to produce almost all the succus entericus, or intestinal 
juice, which is alkaline in reaction, and contains amylolytic 
and sugar-splitting ferments. 

(D) Pancreas. 
Anatomy. — The pancreas is a large gland lying in the upper 
part of the abdominal cavity behind the stomach. It has the 
general shape of a hammer, its head being embraced by the 
bend of the duodenum and its opposite extremity reaching to 
the spleen. It weighs some four or five ounces, and is about 
seven inches long. Its duct, the duct of Wirsung, usually 
joins the common bile duct just where this latter penetrates the 
wall of the duodenum, so that the bile and pancreatic juice 



PANCREAS. 67 

enter the small intestine together. Sometimes the two ducts do 
not join, and sometimes a second smaller duct from the pan- 
creas penetrates the duodenum a little below the large one. 
The duct of Wirsung traced backward divides and subdivides 
until its final ramifications end in the alveoli, or secreting por- 
tions. 

Histology. — This is a compound tubular gland. The cells in 
the alveoli are of the serous type and are granular toward the 
central lumen. During activity they undergo changes very simi- 
lar to the salivary cells, the non-granular zone toward the base- 
ment membrane increasing and extending and the granular zone 

Fig. 21. 





A B 

One Saccule of the Pancreas of the Rabbit in Different States of Activity. 
(From Brubaker after Yeo.) 
A, after a period of rest, in which case the outlines of the cells are indistinct and the inner 
zone — i. e., the part of the cells (a) next the lumen {c) — is broad and filled with fine granules. 
B, after the gland has poured out its secretion, when the cell outlines (d) are clearer, the 
granular zone (a) is smaller, and the clear outer zone is wider. 

becoming correspondingly smaller. Here, as in the salivary 
glands, it is believed that the granules are made from the clear 
protoplasm, and contain the enzymes or their formative mate- 
rials. The formative material in all these glands is given the 
name of zymogen, although the zymogen in a particular gland 
may have a particular name, as pepsinogen, the forerunner of 
pepsin, or trypsinogen, the forerunner of trypsin. 



68 SECRETION. 

Properties and Composition of Pancreatic Juice. — The pan- 
creatic juice is a colorless liquid, alkaline in reaction, and has a 
specific gravity of about 1040 if taken from a recent fistula. It 
coagulates when heated and is prone to putrefaction on exposure. 
With a specific gravity of about 1040, it contains per thousand 
some 900 parts water, the remainder being organic and inor- 
ganic materials in solution. The organic constituents are a 
proteid and three very important digestive ferments, trypsin, 
steapsin and amylopsin. The phosphates and carbonates are 
plentiful and give the fluid its alkaline reaction. 

Method of Secretion. — It can be shown that the secretion be- 
gins to be discharged into the duodenum very soon after the en- 
trance of food into the stomach, and continues as long as intes- 
tinal digestion is in progress. Consequently the flow will be 
intermittent if the meals are far enough apart. It is almost cer- 
tain that the secretion is a reflex act as a result of impressions 
upon the mucous membrane of either the stomach or the duo- 
denum. The acidity of the gastric juice seems to be the natural 
stimulus and to exert its influence upon the duodenal mucous 
membrane. This is not incompatible with the early flow after 
the ingestion of food, for it will be seen later that at least a 
small quantity of that food passes quickly to the duodenum and 
carries gastric juice with it. The composition of the secretion 
seems to be influenced in some degree by the character of the 
food. It is interesting that oils increase the pancreatic flow. 
P?; Nerve Supply. — The pancreas has, besides vaso-motor fibers 
to its vessels, distinct secretory fibers, like those of the salivary 
glands. These fibers probably run in both the sympathetic and 
the vagus. 

Internal Pancreatic Secretion. — Circumstantial evidence 
leaves scarcely any doubt that the pancreas produces some sub- 
stance which is discharged into the blood and markedly influ- 
ences nutrition. Removal of the gland is followed by death 
from inanition in two or three weeks \ and previous to that 



LIVER. 69 

sequel the most striking phenomenon is marked glycosuria, with 
the ordinary symptoms of diabetes mellitus. Retention of a 
comparatively small portion of the gland obviates this condition. 
Sugar does not exist normally in the blood, and this internal 
secretion may contain some ferment which effects its consump- 
tion. 

(E) Liver. 

The liver is the largest gland in the body. Its function is to 
produce bile, glycogen and urea. 

Anatomy, — The liver is situated in the upper part of the ab- 
dominal cavity, chiefly in the right hypocondrium. Its weight in 
the average adult is about four and a half pounds. It is covered, 

Fig. 22. 




The Under Surface of the Liver. 
g. b. t gall-bladder; h. d., common bile-duct ; h. a., hepatic artery; v. p., portal vein; /. 
q., lobulus quadratus; /. s., lobulus spigelii ; /. c, lobulus caudatus ; d. v., ductus venosus ; 
z(. v., umbilical vein. (Kirkes after Noble Smith.) 

except for a small area behind, by peritoneum, processes of which 
run from it at several points and constitute its supporting liga- 
ments. The proper coat of the liver lies underneath the peri- 
toneum, and at the transverse fissure is continued into the gland 
as a sheath, embracing the structures entering there and ramify- 



70 SECRETION. 

ing with them in their distribution. This is the capsule of Glis- 
son. It is fibrous in structure, is closely attached to the liver 
substance, and rather loosely adherent to the structures which 
it envelops. The walls of the portal vein are seen collapsed on 
section, while those of the hepatic veins, which are not sur- 
rounded by Glisson's capsule, and which are closely adherent to 
the gland substance, stand well open. 

A general idea of the liver's anatomy is obtained by noting 
that it has jive lobes, jive fissures, jive ligaments and jive struc- 
tures passing through the transverse fissure. The lobes are 
right, left, caudate, quadrate and Spigelian. The jissures are 
transverse, umbilical, that for the ductus venosus, the fossa for 
the vena cava and the fossa vesicalis. The ligaments are coro- 
nary, right lateral, left lateral, round and suspensory or longi- 
tudinal. The structures passing through the transverse fissure 
are the portal vein, the hepatic artery, the hepatic duct, the 
nerves and the lymphatics. 

Blood-vessels. — Of the two blood-vessels entering the fissure 
the portal vein is decidedly the larger. It has collected the 
blood from the abdominal organs by the radicles of its tribu- 
taries, the gastric, splenic, superior and inferior mesenteric 
veins, while the hepatic artery is a branch of the celiac axis. 
These, having been distributed in a manner to be noted pres- 
ently, discharge their blood- into the radicles of the hepatic 
veins, which, usually three in number, enter the ascending vena 
cava, where that vessel passes through the liver behind. Again, 
it is to be remembered that these two vessels, as well as the 
nerves and lymphatics, are enveloped in the vagina, or capsule 
of Glisson. 

The portal vein and the hepatic artery give off branches to 
the capsule of Glisson, constituting the vaginal plexus. The 
portal vein, still ensheathed, then divides and subdivides until 
its branches run directly between the lobules, and are called in- 
terlobular veins. These direct subdivisions of the portal vein 



LIVER. 



71 



are not the only interlobular veins, however. Those branches of 
this vein which were given off to the capsule of Glisson, having 
received the corresponding branches from the hepatic artery, 
also here run between the lobules and make part of the inter- 
lobular plexus. The interlobular veins, thus surrounding the 
lobules and having lobules on either side of them, give off in 

Fig. 23. 




Diagram of the Portal Vein, 
(J>v) arising in the alimentary tract and spleen (s) and carrying the blood from these 
organs to the liver. (From Brubaker after Yeo.) 

both directions branches (lobular branches) which penetrate the 
lobules, to break up into capillaries. The capillaries finally 
converge to three or four small radicles, which in turn unite to 
form a small vein in the center of the lobule. This is the in- 
tralobular vein, which at the base of the lobule joins the sub- 



72 



SECRETION. 



lobular vein. These sublobular veins join each other to form 
hepatic veins, which become larger and larger until they have 
collected all the blood which has entered the liver. They 
finally enter the ascending vena cava. 

But what has become of the hepatic artery ? As soon as it 

Fig. 24. 




Section of Lobule of Liver of Rabbit in which the Blood Capillaries and Bile 

Canaliculi have been Injected. (From Yeo after Cadiat.) 
a, intralobular vein; b, interlobular veins ; c, biliary canals beginning in fine capillaries. 



LIVER. 73 

has entered the sheath, it gives off branches to the capsule 
forming part of the vaginal plexus and entering into the vaginal 
branches of the portal vein just before these run between the 
lobules. It also furnishes branches to the wall of the portal 
vein, to the walls of the larger divisions of the artery itself, and 
to the hepatic duct. 

Histology of a Lobule. — The liver is made up of a large number 
of lobules about one twenty-fifth of an inch in diameter, 
separated by vessels, nerves and radicles of the hepatic duct. 
Such a lobule in certain of the lower animals has a distinct 
polygonal shape, but in man the outlines are not clear. In the 
lobule are the hepatic cells, ovoid in shape, possessed of small 
granules and one or two nuclei. They are disposed in columns 
radiating from the central intralobular vein. These cells belong 
to the epithelial type, and the liver is not essentially different 
from other glands, such as the salivary, except in the complexity 
of its arrangement. The analogy is established by the origin of 
the bile ducts in the lobules between the cells. 

Bile Ducts. — It is not difficult to demonstrate the interlobu- 
lar ducts, but to follow them as such into the lobule is less 
easy. However, there is no doubt at all that they do origi- 
nate between the hepatic cells. It is probable that here they 
have no distinct lining membrane, but are mere tubular inter- 
cellular spaces, into which the bile is poured and carried into 
the interlobular duct. Typically a liver cell has one of these 
bile capillaries on one side and a blood capillary on the other, 
and while this relation does not always hold good, every cell 
does communicate with both kinds of capillaries. The inter- 
lobular bile ducts consist of epithelium resting upon a very 
thin basement membrane. As they increase in size they gain 
fibrous inelastic and elastic tissue, and the largest some non- 
striated muscular elements. Gradually as the ducts become 
larger the lining epithelium changes from the columnar to the 
pavement form. Mucous glands exist in the largest ducts. 



74 



SECRETION. 



The interlobular ducts join each other and gradually increase in 
size as they merge from all parts of the liver, to leave its sub- 
stance in two divisions — one from the right and one from the 
left lobe. These two unite to form the hepatic duct which, 
running a course of about one and a half inches, is joined at an 
acute angle by the cystic duct to form the common bile duct, 



terlobular con- 
ive tissue. 




From a Horizontal Section of Human Liver. X 4°- 
Three central veins, cut transversely, represent each a center of as many hepatic lobules, 
that at the periphery are but slightly defined from their neighbors. Below and to the right of 
the section the lobules are cut obliquely and their boundaries cannot be distinguished. 
(From Stohr.) 

or the ductus communis choledochus. This last penetrates 
obliquely the duodenal wall and discharges the bile into the in- 
testine. The cystic duct has its origin at the apex of the gall 
bladder, and is about one inch long. The common bile duct 
has an average length of three inches. (See Fig. 22.) 

Gall Bladder. — The gall bladder has an oval shape with its 
arge end forward. It is on the under surface of the liver, the 



LIVER. 75 

peritoneum running over (or rather under) it. It has a mucous 
lining and the remainder of its structure is chiefly fibrous. A 
little plain muscular tissue may exist. Its capacity is about one 
and a half ounces. Mucous glands are found in its lining, as in 
that of the large ducts, and these are responsible for the mucin 
of the bile. 

Hepatic Nerves. — With regard to the exact destination of 
the nerves entering the liver, little is known. Evidence going 
to establish the termination of fibers in the cells, that is, the 
existence of distinct secretory fibers, is meager. There is little 
doubt that secretory fibers for the glycogenic function of the 
liver do exist. It is known that fibers from the vagus, phrenic 
and solar plexus enter the fissure, but they cannot be followed 
farther than the ramifications of Glisson's capsule between the 
lobules. Of course, vasomotor fibers go to the vessels, as else- 
where. Fibers acting similarly go also to the muscular tissue of 
the large ducts and of the gall bladder. The contraction of the 
gall bladder is thought to be reflex, afferent impressions being 
conveyed by the vagus from the mucous membrane of the duo- 
denum. 

Hepatic Lymphatics. — The lymphatics are abundant, and 
those not originating in the connective tissue are thought to 
originate by perivascular canals surrounding the blood-vessels 
of the lobules. The fact that when the outflow of bile is oc- 
cluded it passes, not into the vascular, but into the lymphatic 
circulation is a curious circumstance. It may be due to the 
absence of a definite wall for the intralobular ducts and their 
comparatively free communication with the lymphatics in those 
localities. 

Properties and Composition of Bile. — Human bile is of a 
dark greenish-red color, has a bitter taste and is practically 
odorless when fresh. It undergoes putrefaction easily, but is 
not coagulable by heat. It is viscid, chiefly on account of the 
mucin it contains. It has an alkaline reaction, and a specific 



76 SECRETION. 

gravity of about 1030. Besides water, which constitutes more 
than ninety per cent, of its bulk, it contains the sodium salts of 
taurocholic acid and glycocholic acid (the biliary salts), cho- 
lesterin, bilirubin, lecithin, fats, soaps, mucin and various inor- 
ganic salts, such as sulphates, carbonates, phosphates, etc., and 
a quantity of carbon dioxide. The quantity of bile secreted in 
twenty-four hours is about two and a half pounds. 

In human bile sodium taurocholate largely predominates 
over glycocholate. These are formed as acids by the liver cells, 
are absorbed in their passage down the intestine, and are pre- 
sumably those parts of the bile which are concerned in its digestive 
action, particularly in the absorption of fats. So far as these 
constituents are concerned, the bile is a typical secretion. 

Cholesterin, on the other hand, seems to be simply removed 
from the blood by the liver cells, and is discharged in the feces, 
where, however, it exists in a slightly changed form, stercorin. 
It is thought to be held in solution by the bile acids, glycocholic 
and taurocholic. So far as this constituent is concerned, there- 
fore, the bile is a typical excretion. It is produced in many of 
the body tissues, and no function has been discovered for it. 

Bilirubin is the characteristic coloring matter of the human 
bile ; that of herbivorous animals is biliverdin, and a little of 
this latter is also present in human bile. These pigments 
originate from hemoglobin. It is supposed that when the red 
corpuscles break down, " the hemoglobin is brought to the liver, 
and then under the influence of the liver cells is converted into 
an iron-free compound, bilirubin or biliverdin." (Howell.) 

The lecithin is probably an end product of physiological 
activity in the tissues, and is apparently an excretion. 

The mucin gives the fluid its viscid character. 

The production of bile is continuous, but this does not 
mean that its discharge into the duodenum is continuous, for 
in the intervals of digestion it is not admitted (freely at 
least) into the intestine, but regurgitates from the ductus com- 



LIVER. 77 

munis choledochus through the cystic duct into the gall bladder, 
which acts as a reservoir until its contents are needed. The 
secretion is more active, however, during intestinal digestion 
than at other times. This appears to be reflex, but may be 
simply a result of the increased amount of blood passing 
through the portal vein to the liver during that period, for the 
whole alimentary canal is congested while digestive activity is 
in progress. Again, it is known that the best cholagogue is bile 
itself, and some of the bile is absorbed in its passage down the 
intestine. Its presence in the blood may account for the accel- 
erated flow. 

Method of Secretion and Discharge. — The bile is a product 
of the liver cells. How they receive their normal stimulus is 
obscure. But it is reasonable to suppose that a larger supply of 
blood means a more abundant secretion. Such an increase of 
blood supply occurs during digestion. 

The cells discharge the bile into the bile capillaries, which 
pass it onward either to the intestine directly or, during the 
intervals of digestion, to the gall bladder. When food enters 
the duodenum, a reflex influence causes the wall of the gall 
bladder to contract and compress its contents. The only out- 
let is through the cystic duct into the common duct, and thence 
into the duodenum. This reflex does not take place until food 
has entered the duodenum, and of different foods it is found that 
proteids (peptones) and fats are the most efficient stimuli. 

The secretion of bile is not stopped by ligation of either the 
portal vein or the hepatic artery, showing that both of these 
vessels contain bile materials. But it would be unreasonable to 
suppose that the blood of the portal vein does not furnish the 
bulk of secreting material. 

The function of bile will be referred to under Digestion. 

Glycogenic Function. — The formation of glycogen is con- 
nected with nutrition, but will receive some notice here. This 
is an internal secretion. It is produced by the liver cells, and 



7§ 



SECRETION. 



can be demonstrated in their substance by the microscope and 
by chemical reagents. It can also be shown to increase markedly 
after eating, and to decrease notably when eating is refrained 
from for some time. 

Glycogen is a carbohydrate very similar to starch, and when 
ingested it is acted upon by the same enzymes and undergoes 
the same conversions. Furthermore, the amount of glycogen 
in the liver is very greatly increased by restricting the diet to 
carbohydrate foods and is lessened considerably below the nor- 
mal (that is, its amount on a mixed diet), but is not reduced to 
zero, when proteids alone are taken. This points to the con- 
clusion that the source of glycogen is carbohydrates, but that it 
can be formed to some extent from proteids. Let it be said 
now that practically all carbohydrates are converted by digestion 
into maltose, or maltose and dextrin and furthermore that during 
absorption these sugars are converted into dextrose or dextrose 
and levulose. It is customary to assume that the digestion of a 
carbohydrate means its conversion into dextrose (glucose, levu- 
lose). It is, then, this sugar which is carried to the liver by 
the portal vein. 

We may say that the formula for dextrose is C 6 H 12 6 and for 
glycogen C 6 H 10 O 5 , though neither of these formulae is probably 
exactly correct. It will be seen, therefore, that the abstraction of 
one molecule of water (H 2 0) from dextrose will produce glycogen, 
and this is the change which the liver cells are supposed to effect. 
Again, when the conversion of dextrose into glycogen has taken 
place, the glycogen is stored up in the liver cells, to be given off 
continuously to the blood only in such quantities as the system 
may demand. The liver thus becomes a warehouse for the stor- 
age of all the carbohydrates. 

It will be seen under Nutrition that the carbohydrates furnish 
the chief material to be burned up in the body for the purpose 
of liberating heat and furnishing energy, and if they should be 
consumed as soon as they enter the circulation, there would be 



LIVER. 79 

not only an unnecessary waste during their quick consumption, 
but also an unfortunate lack of energy-producing materials 
before another meal. This storing up brings about a kind 
of conservation of energy and an economical regulation of its 
distribution. The amount of sugar in the circulation at any time 
is very small, and a single carbohydrate meal may, by the action 
of the liver, be made to supply the carbohydrate demands of the 
tissues for a considerable period. 

Now, it was just said that the sugar of the blood is dextrose ; 
if the dextrose of the portal blood is converted into glycogen to 
be stored up, it must be reconverted i7ito dextrose before it can 
leave the liver, since it leaves by the blood. The cells do effect 
the second conversion, and this is the second part of the glyco- 
genic function. It may be that the liver cells produce an en- 
zyme corresponding to ptyalin, which converts the glycogen. 
Dextrose does not normally exist in the liver cells. At the very 
moment of its formation it is carried away by the blood. 

The fact that the liver can form glycogen out of proteids 
shows, of course, that the nitrogen is eliminated from the proteid 
molecule in some way. A carbohydrate molecule is left to be 
oxidized in the usual manner. This is thought to be the initial 
step in the final consumption of proteids innutrition. The fats 
have no influence on glycogen formation. 

Glycogen also exists in other parts of the body, particularly 
in the voluntary muscular substance. The cells of the tissues in 
which it is found must also have a glycogenic function. 

Urea Formation. — But the liver has another function besides 
the production of bile and glycogen, and that is to form urea. 
It will be seen later that the chief end product of proteid metab- 
olism is urea, and that it is eliminated almost entirely by the 
kidneys. The liver is much more active in the production of 
this substance when the portal blood is charged with digested 
materials, but it also forms urea in fasting animals. The liver 
must therefore be capable of forming urea from some of the prod- 



80 SECRETION. 

ucts of digested foods. With reference to its formation in 
fasting animals, suffice it to say here that it seems that as long as 
proteid metabolism goes on in other tissues, there are produced 
in those tissues materials (ammonia compounds) which, when 
carried to the liver, are converted by it into urea. Further notice 
will be given to this phase of the subject under Nutrition. 

The liver cells produce urea ; it enters the blood, is carried to 
the kidneys and eliminated by those organs. In the mechanism 
of its production and discharge from the liver, it thus corresponds 
to the internal secretions, though urea is distinctly an excretion. 

It must not be supposed, however, that the liver is the only 
organ producing urea. There are other organs which certainly 
produce it, while there are those who maintain that it is pro- 
duced directly wherever proteid metabolism is in progress. 

(F) Sebaceous Glands. 

The sebaceous glands (see Hair-follicles) are chiefly associated 
with hair-follicles and, existing wherever hair is to be found, 
cover well-nigh the whole cutaneous surface. They are of the 
simple or compound tubular type, and discharge their secretion 
into the hair-follicle near its outer extremity. The alveoli are 
lined by several layers of cuboidal epithelial cells. The cells 
of the layer nearest the lumen contain fatty matter, and are 
thought to form the secretion by breaking down and being 
thrown off themselves. Their place is taken by cells from the 
deeper layers, which undergo similar changes and disintegrate. 

Composition and Properties of Sebum. — Chemically sebum 
is largely made up of fatty matters. It also contains choles- 
terin, which is in combination with a fatty acid. It forms a thin 
coating over the cutaneous surface, accounting for the normal 
oiliness of the skin. It also contributes to the characteristic 
softness of the hairs, and prevents their breaking off from 
brittleness. Its presence over the body surface may have some 
influence in regulating the loss of heat by evaporation. 



SEBACEOUS AND MAMMARY GLANDS. 8 1 

Cerumen, smegma and the secretion from the Nabothian 
glands are only modified forms of sebum, and the structures 
producing these secretions belong to the class of sebaceous 
glands. 

(G) Mammary Glands. 

Structure. — The mammary glands are two in number in the 
human being, and are loosely attached to the great pectoral 
muscles. They are rudimentary in both sexes until puberty, 
and in men throughout life. At puberty the gland in the female 
enlarges markedly, but is never fully developed before preg- 
nancy. At this time the gland vesicles make their appearance, 
and the rudimentary ducts come to be more and more ramified. 
These ramifications do not reach their full development, how- 
ever, until lactation begins. The skin covering the areola of 
the nipple is dark, especially during pregnancy, and much 
thinner than over other parts. The dark color is due to a de- 
posit of pigment. 

The mammary gland belongs to the compound tubulo-racemose 
type, and consists of fifteen or twenty lobes bound together by 
areolar connective tissue. Each lobe is made up of a number of 
lobules, containing the alveoli or secreting portions. The 
secretion from all the alveoli and lobules of a lobe converges to 
a single duct, which discharges its contents upon the surface of 
the nipple without anastomosis with any other duct. There are, 
therefore, some fifteen or twenty ducts thus opening upon the 
surface. Each of them has a dilatation beneath the nipple, and 
it is in these sinuses largely that the milk accumulates during 
lactation. When lactation has ceased the ducts retract, the 
sinuses disappear, the alveoli undergo retrograde changes, and 
the whole gland is inclined to become flabby and pendulous. 
It does not regain after pregnancy the firmness which character- 
ized it before. 

Secretion of Milk. — After parturition the first discharge from 
the gland is colostrum, a liquid resembling milk in some respects. 



82 SECRETION. 

In two or three days the true milk appears. Besides water 
and inorganic salts, all the constituents of milk are formed by 
the cells of the mammary gland. During the period of gestation 
the cells lining the alveoli are flat and have only a single nucleus. 
When they begin to secrete they increase in height, the nuclei 
divide and that portion of the cell toward the lumen undergoes 
fatty degeneration. This fatty material is extruded into the lumen 
and apparently constitutes a part of the secretion. The liquid 
constituents taken out of the blood probably hold the proteid 
and carbohydrate portions in solution, while the fatty particles 
constitute the fat of the milk. Thus secreted, the liquid accumu- 
lates in the ducts and sinuses until removed by the infant or 
otherwise. The fact that the secretion of milk in woman is in- 
fluenced by emotions of fear, grief, etc., is strong evidence of a 
nervous control of the procedure, but proof of secretory fibers to 
the cells has not been established. 

The quantity of food required by the mother during the time 
the child is nursed is increased, but no particular kind of food 
seems to be especially required. The larger demand for liquids 
is marked, however, and when the quantity of milk is increased 
by a large ingestion of liquids, the solids in the secretion are 
not relatively diminished. 

Composition and Properties of Milk. — Human milk has a 
specific gravity of about 1030, and is not so white or so opaque 
as cow's milk. Besides water, its chief constituents are fats, lec- 
ithin, cholesterin, casein and lactose, of which the two last 
named are the most important. Casein is the main proteid con- 
stituent. Lactose is very abundant, and is responsible for the 
sweet taste and for a large part of the nutritive value of the fluid. 

(H) Thyroid Gland. 

The thyroid gland consists of two glandular masses united by 
an isthmus of the same structure. It lies in front of the trachea 
at the lower end of the larynx. It consists of a large number 



THYROID AND ADRENAL GLANDS. 83 

of vesicles bound together by connective tissue. Each vesicle 
is lined by cuboidal epithelial cells, which secrete a semi-gelati- 
nous substance, colloid. 

It has long been known that the removal of the whole thyroid 
gland, including the parathyroid, occasioned marked interfer- 
ence with nutrition and other changes, the chief of which are 
disturbances of muscular coordination, possibly convulsions, 
emaciation, apathy, and subsequent death. There is no duct 
connected with the gland, and the secretion is therefore an in- 
ternal one. Very little is known of it except that it is necessary 
to the maintenance of life. If a very little of the gland be left, 
or if, after its complete removal, a small bit of it be transplanted 
in some other part of the body, or if the animal be fed on the 
thyroid extract or the fresh gland, the characteristic symptoms 
do not ensue. 

The muscular disturbances direct the attention to the central 
nervous system when an attempt is made to explain the occur- 
rences, and it is not improbable that the effect of the thyroid 
secretion is in some way exerted upon or through the central 
system. It seems generally agreed that the thyroid does dis- 
charge a secretion into the blood and that it is the withdrawal 
of some part of that secretion from the circulation which is re- 
sponsible for the remarkable train of symptoms sequent upon its 
removal. This essential constituent is regarded by some as 
being an agent which destroys certain toxic principles in the 
blood, by others as being requisite to the metabolic functions in 
the body without destroying anything. Baumann has isolated 
from the gland substance a material containing a large propor- 
tion of iodine, to which he gives the name iodothyrin, and it is 
very probable that this is one, at least, of the beneficial sub- 
stances in the thyroid secretion. 

(I) Adrenal Glands. 
The adrenal glands or suprarenal capsules, resting upon the 
upper ends of the kidneys, are ductless glands whose removal is 



84 SECRETION. 

followed by weakness, impaired nutrition and disturbances in the 
circulation. Death usually supervenes in two to four days. 
These bodies must produce an internal secretion which is re- 
moved by way of the adrenal veins. It may destroy toxic sub- 
stances in the blood. A solution injected into the circulation 
certainly affects the middle wall of the vessels, causing contrac- 
tion, and a heightened pressure. The heart is also notably in- 
hibited. It is not thought that the effect on the vessels is brought 
about through the vaso-motor nerves, but by direct excitation of 
the muscular substance. Little in fact is known about the secre- 
tion, except that it is necessary to life. Abel has isolated an 
alkaloid, epinephrine, which is claimed to be the active principle. 
These glands are the seat of lesions in Addison's disease, and 
many cases of this malady are at least favorably influenced by 
the use of adrenal extract. 

(J) Pituitary Body. 
The pituitary body lying in the sella turcica on the superior 
surface of the sphenoid bone, also produces an internal secretion 
of physiological value. Its removal is regarded as causing death. 
Howell has shown that injection of extract from the posterior 
division occasions a rise of temperature and slowing of the heart. 
Its situation makes satisfactory experiments very difficult. 

(K) Testis and Ovary. 
The testes and ovaries, though not probably true glands, 
also may produce an internal secretion of obscure physiological 
value. It is not essential to life. Injections of extracts from 
these bodies are claimed to have a remarkable stimulating effect 
upon the nervous and muscular systems. In mental and physical 
disturbances occasionally following removal of the ovaries, gyne- 
cologists often find administration of the ovarian extract to be 
beneficial. 



CHAPTER IV. 
FOODS, DIGESTION AND ABSORPTION. 

(A) FOODS. 

It is evident that all the tissues of the body are continually 
undergoing "physiological wear" — that the materials of which 
they are intrinsically composed are being changed into effete 
matter and discharged from the system. This is a process going 
on in the substance of every cell in the body, and obviously 
for these cells to continue to live and functionate there must be 
a continual appropriation of new matter to take the place of 
the materials which have served their physiological purpose, and 
are therefore now useless. Such supply is made directly to the 
tissues by the blood, but lest this fluid be impoverished, it must 
in turn be furnished with an approximately constant quantity of 
nutritive matter. The ultimate source of that matter is in the 
food we eat, though of course it must pass through the processes 
of digestion and absorption. This conception of a food must 
be understood to embrace all substances contributing, either di- 
rectly or indirectly, to body nutrition, including, therefore, 
the oxygen of the air as well as all articles usually classed as 
drinks. 

An animal whose weight remains about the same must eat and 
digest a certain quantity of food to keep up the body tempera- 
ture, to supply mechanical energy, and to repair the wastes 
which go on even during sleep. An animal which is growing 
and increasing in weight must eat enough not only to supply 
the demands just mentioned, but also to be stored up as new 
tissue when properly transformed. It will be seen that the arti- 

85 



86 FOODS. 

cles we eat, besides being largely insoluble, differ very ma- 
terially in their composition from any substances found as parts 
of the body tissues, and also that even those undigested sub- 
stances most closely resembling living tissue will not be utilized 
by the cells when presented to them (injected) in the usual ve- 
hicle, the blood. 

Seat of Hunger. — Food is taken into the body in obedience 
to an expressed want on the part of the system. The desire for 
food — the sensation of hunger — is referred in a rather indefinite 
way to the stomach. But because that sensation is ordinarily 
satisfied by the introduction of food into the stomach does not 
argue that its seat is in that organ. Removal of the stomach by 
no means prevents hunger, but if nutritious materials be intro- 
duced in sufficient quantity into the circulation, as by rectal 
enemata, hunger is relieved. The true seat of this sensation is 
undoubtedly in the cells themselves, it being simply a call from 
them for more material to take the place of their worn-out con- 
stituents. 

Cold weather demands an increase in the amount of food, as 
also do physical and psychical activity, certain drugs, etc. 

Seat of Thirst. — The demand of the cells for water is referred 
to the fauces and throat, but this is no more the seat of thirst 
than is the stomach of hunger. The taking of water into the 
mouth alone will not quench thirst, except in so far as absorp- 
tion may take place from the mucous membrane. But if water 
in sufficient amount be gotten into the circulation in any way 
satisfaction ensues. Next to the demand for oxygen, that for 
water is the most imperative which comes from the tissues ; that 
is, they can live much longer without solid food than without 
water. The amount necessary is manifestly subject to many 
conditions, such as external moisture and temperature, exercise, 
etc. 

Classification of Foods. — A very large number of substances 
are taken into the alimentary canal as food ; but examination 



CLASSIFICATION OF FOODS. 87 

reveals that all such materials contain one or more of a very 
few classes of alimentary principles or food stuffs. The foods 
are classed as : 

I. Salts and Water (inorganic). 
II. Proteids, Albuminoids (organic nitrogenous). 

III. Carbohydrates (organic non-nitrogenous). 

IV. Fats (organic non -nitrogenous) . 

I. The inorganic salts and water are scarcely looked upon 
as food in the common acceptation of the term, but they are 
quite as necessary to cell life as any of the other classes. They 
constitute an unimportant factor in the process of digestion and 
receive little attention in a discussion of that subject, because 
they really do not undergo digestion at all, but are simply dis- 
solved in the fluids of the alimentary tract, absorbed and dis- 
charged from the system in the same shape in which they 
entered. Such as cannot be dissolved in the gastro -intestinal 
media are never absorbed. It is evident that much of this class 
is ingested with II., III. and IV. In fact, all the proteids have 
combined with them inorganic materials, from which they are 
not separated by digestion ; the two are deposited and dis- 
charged together from the system. It is seen that this class 
corresponds to the binary proximate principles, and they are 
treated of somewhat more in detail under the Chemistry of the 
Body. Suffice it to say, that, excepting water and common 
salt, our ordinary foods furnish a sufficient supply of the inor- 
ganic principles. 

II. The proteids, corresponding to the quaternary proxi- 
mate principles, are of different varieties, but all are of ap- 
proximately the same food value, and indeed cannot be studied 
separately. They are contained in both animal and vegetable 
diets, but usually the main part of our proteid income is in 
meat. They are the most important of the food stuffs because 
they are the only ones containing nitrogen, and they are there- 
fore the only ones capable of repairing tissue wastes or building 



88 FOODS. 

up new tissue. Under the consideration of Nutrition it will be 
seen that the proteids, besides being useful in constructive metab- 
olism, are also of value in furnishing bodily energy and heat. 
It is unnecessary to add that this is the only class of foods capa- 
ble alone of sustaining life, for vital activity means protoplasm, 
and protoplasm is nitrogenous in composition. Proteid is an 
absolute necessity ; the other foods are only accessory to this 
class. 

Special attention is called to the fact that while the albumi- 
noids are not here differentiated from the proteids, they prop- 
erly belong in a class by themselves. They contain nitrogen, 
and therefore resemble the proteids in chemical composition, 
but they are incapable alone of sustaining life, and therefore 
resemble the carbohydrates and fats in their physiological value. 
Gelatin is a typical example of the albuminoids. As a class 
they do not exist to any considerable extent in the articles we 
eat, and in this work the terms " nitrogenous " and " proteid " 
foods will be considered synonymous, and the true albuminoids 
will be largely disregarded. 

III. The Carbohydrates, representing part of the ternary 
proximate principles, include the starches, sugars, gums, etc., 
already referred to. They are of definite chemical composition 
and contain no nitrogen. They are contained in fruits, vege- 
tables, especially in cereals, and in some animal foods, such 
as milk, honey, liver, etc. They are the cheapest foods from 
financial and digestive standpoints and constitute the main bulk 
of articles eaten. They contain more oxygen than do the fats, 
and are more easily oxidized and converted into heat and mus- 
cular energy. In fact, their great physiological value lies in the 
ease with which they are thus burned up in the body. They 
furnish the main part of the fuel necessary to the running of the 
animal mechanism. 

iV. The fats, representing the other part of the ternary 
proximate principles, are ingested with both animal and vege- 



DIGESTION. 89 

table diets. Animal fat, seeds, grains, nuts and certain fruits 
and cereals furnish in most part this class of our foods. The 
fats contain no nitrogen, and, like carbohydrates, their great 
physiological value lies in the fact that they are destroyed in the 
organism to produce energy, whether in the form of heat or 
muscular exercise. They are handled and converted less readily 
by the system than the carbohydrates, and consequently tax the 
digestive powers more. But it is found that, weight for weight, 
they are more efficient in the production of energy than are the 
carbohydrates. They also furnish fuel for the running of the 
body mechanism. How the reserve energy of the body is stored 
up in fat will receive later notice. 

Now, the articles we ordinarily take as food contain usually all 
the above classes, together with innutritious and indigestible 
materials from which they must be separated. The animal foods, 
particularly eggs and the muscular substance, are character- 
ized by the small amount of carbohydrate and the large amount 
of proteid substance entering into their composition. Of the 
meats, beef especially contains much proteid. As a rule vege- 
tables contain much carbohydrate, but also quite a quantity 
of proteid matter. Peas, beans, etc., contain much proteid. 
But it is not to be forgotten that nutrition is effected not by 
what is eaten but by what is absorbed. It is found that the 
animal proteid foods are usually more completely digested and 
absorbed than are the vegetable. 

(For amount and kind of food necessary see Nutrition.) 

(B) DIGESTION. 

Object. — Digestion is largely a chemical process. Certain 
physical phenomena are auxiliary. The inorganic foods are 
not affected in a chemical way by digestion. They are simply 
dissolved, if not already in solution, and are discharged from 
the body in the same condition in which they entered. But the 
other classes of food must either be separated from innutritious 



90 DIGESTION. 

substances with which they enter, or undergo certain changes 
themselves, or both, before they can be absorbed and assimilated. 
This necessitates a complicated digestive apparatus and the sub- 
jecting of different classes of food to different digestive fluids and 
other gastro-intestinal influences. The object of digestion is there- 
fore twofold, first y to convert the foods into soluble materials and, 
second, to bring about such changes in their composition as will 
insure their absorption and appropriation by the tissues. 

Enzymes. — The chemical changes taking place in digestion 
are of a peculiar nature, in that they are effected largely by the 
presence of substances known as enzymes, corresponding in an 
obscure way with ordinary chemical reagents. These have been 
called unorganized or unformed ferments, to distinguish them 
from such organized ferments as bacteria, yeast, fungi, etc. 
They are not themselves possessed of any vital activity, though 
formed in living organisms, like plants or animals. They are 
of indefinite chemical composition, contain nitrogen and are 
supposed to be of proteid structure. The characteristic point in 
their action has been supposed to be that they produce a chem- 
ical change without themselves being affected by that change. This 
is doubtless practically true, but it is found in experimental work 
that " a given solution of enzyme cannot be used over and over 
again indefinitely. ' ' It finally loses its identity. 

According to the foods on which they act and the effects they 
produce, enzymes are classified as: (i) Proteolytic enzymes. 
These convert proteids into soluble peptones ; examples are 
pepsin and trypsin. (2) Amylolytic enzymes. These con- 
vert starches into sugar; examples are ptyalin and amylopsin. 
(3) Fat-splitting enzymes. These convert neutral fats into 
glycerine and fatty acids; an example is steapsin. (4) Sugar- 
splitting enzymes. These convert the non-absorbable (sac- 
charose) into absorbable (dextrose) sugars ; an example is 
invertase. (5) Coagulating enzymes. These precipitate solu- 
ble proteids ; an example is rennin. 



ENZYMES. 91 

Characteristics of Enzymes. — Some of the characteristics of 
enzymes are as follows : (1) They are soluble in water and in 
glycerine. (2) In solution they are destroyed before the boil- 
ing point is reached (140 to 180 Fahrenheit). Very low 
temperatures do not destroy them, but suspend their action. (3) 
They never completely convert the substance upon which they act 
(unless it be the fifth class). It is supposed that the substance 
produced, as peptones for example, have an inhibitory action 
upon the enzyme. If they are removed as they are formed, the 
action of the enzyme continues. (4) The particular result is in- 
dependent of the amount of the enzyme (unless it be very 
small) no matter how large a quantity of the substance to be 
acted upon is present. 

Manner of Action. — These enzymes are supposed to bring 
about their respective changes through hydrolysis — that is, by 
causing water to be taken up by the molecules of the affected 
substance and by the subsequent splitting of the newly formed 
molecule into two or more simpler ones. How they cause this 
appropriation of water is as yet undetermined. It was formerly 
supposed to be brought about by contact merely, and the 
enzymes were called catalytics ; but this term offers no explana- 
tion of the real change which occurs. 

This much seems necessary to be said about enzymes, that a 
more intelligent understanding may be had of the part they play 
in digestion. The facts in regard to them as above enumerated 
are gathered mainly from Howell. 

Digestive Processes. — The digestive processes may be con- 
sidered under the heads of (1} prehension, (2) mastication, (3) 
insalivation, (4) deglutition, (5) gastric digestion and (6) in- 
testinal digestion. Prehension, mastication and deglutition can- 
not properly be looked upon as digestive processes, inasmuch as 
they involve no chemical change. They are, however, neces- 
sary occurrences, and cannot be disregarded. Of course, ab- 
sorption and "internal digestion" are supposed to follow gas- 
trointestinal or "external digestion." 



92 DIGESTION. 

Prehension. 
Prehension is simply the taking of food into the mouth. Its 
mechanism in the human adult is so familiar that it needs no 
description. In the sucking child it is more complex. The 
buccal cavity is closed posteriorly by the application of the 
velum palati to the base of the tongue. The tip of the tongue 
is applied to the hard palate, and successive portions of it (go- 
ing backward) being applied in the same way leave a vacuum in 
front, and liquids are drawn into the mouth. The mechanism 
of drinking is the same. 

Mastication, 

Object. — The object of mastication is to grind up the food 
that it may be swallowed, and that the various digestive fluids, 
particularly the saliva and gastric juice, may have more ready 
access to its parts. To pass to the stomach food which has been 
improperly triturated and insalivated is to tax that organ un- 
necessarily, and this is not infrequently an important etiological 
factor in dyspepsia. 

Mechanism. — Mechanically, mastication is effected by the 
action of the lower jaw, aided by the tongue, lips and cheeks. 
This remark presumes of course that the teeth are intact. Lat- 
eral and antero-posterior movements of the inferior maxilla 
combine with its simple elevation to compress and grind the 
food between the teeth. The muscles which depress the lower 
jaw are the digastric, mylohyoid, geniohyoid and platysma. 
Those which elevate it are the temporal, masseter, internal and 
external pterygoids. The attachments of the external ptery- 
goids are such that by their simultaneous action the maxilla can 
be thrown forward and by their alternate contraction from side 
to side. The tongue is active during mastication in carrying 
the mass to this or that part of the buccal cavity that it may be 
completely comminuted. It also gives accurate information as 
to the size and stage of mastication, insalivation, etc., of the 



INSALIVATION. 93 

bolus in the mouth. The cheeks, as is shown in facial palsy, 
are quite important in keeping the food from between them and 
the teeth. The lips prevent the escape of liquids from the 
mouth, besides assisting in prehension. 

Insalivation. 

Insalivation and mastication go on together. For the his- 
tological structure of the salivary glands and general properties 
of saliva, together with the mechanism of secretion, see section 
on Secretion, page 55 et seq. We are concerned here with its 
digestive properties only. 

Composition of Saliva.— Chemically, it consists per thousand 
of about 994 parts water and six parts solids — these solids be- 
ing chiefly mucin, ptyalin, albumin and inorganic salts. The 
inorganic salts are mainly the chlorides of sodium and potas- 
sium, the sulphates of potassium, the phosphates of potassium, 
sodium, calcium and magnesium, and sulphocyanide of potas 
sium. The mucin gives the ropy consistence to the fluid and 
serves a mechanical purpose only. The sulphocyanide of potas- 
sium is unusual in the body secretions, and its presence here is 
interesting. It may represent an end product of proteid metab- 
olism. The true digestive value of saliva is due to ptyalin, 
an amylolytic enzyme. 

Function.— The function of this secretion is twofold, (a) 
mechanical and (b ) chemical. 

(#) From a mechanical standpoint (1) it facilitates phona- 
tion, mastication and gustation by maintaining a proper degree 
of moisture in the mouth; (2) its more watery parts (parotid) 
mix with the food, dissolving part of it, so that it may be more 
easily masticated and swallowed while its more viscid parts 
(submaxillary and sublingual) spread over the surface of the 
bolus to aid in deglutition. 

(b ) From a chemical standpoint, the function of the saliva 
is to convert starch into sugar. It does this through the agency 



94 DIGESTION. 

of its enzyme, ptyalin, which conforms to the characteristics 
of enzymes already noted. Maltose (C 12 H 22 O u + H 2 0) is the 
form of sugar produced, but there are several intermediate sub- 
stances formed before maltose finally results. The starch mole- 
cule (C 6 H 10 O 5 ) was formerly supposed to simply appropriate a 
molecule of water to form dextrose (grape sugar, glucose, C 6 H ]2 - 
6 ), but it is now thought that there is a succession of hydrolytic 
changes with the production of dextrin and maltose. That is, 
the starch molecule appropriates a molecule of water ; this new 
molecule splits into a certain kind of dextrin and maltose \ the 
dextrin left itself appropriates water and splits up into another 
kind of dextrin and maltose ; this last dextrin goes through a 
similar process with a like result, until finally only maltose is 
produced. Some dextrose may be produced. It will be seen 
under gastric digestion that mineral acidity will also convert 
starch into sugar, but in this case the form of sugar is dextrose. 

The effect of temperature on the action of enzymes has been 
noticed. The optimum for ptyalin is ioo° Fahrenheit. The 
reaction of saliva is alkaline and its effect on starch is stopped 
by an acid medium, since the enzyme is thereby destroyed. 
However, ptyalin has been shown to act even a little better in 
perfectly neutral than in alkaline solutions (Chittenden). The 
action of this substance on starch is very much facilitated if the 
starch be cooked ; in fact, its action on uncooked starch is so 
slow as probably to be inconsequential in digestion. Cooked 
starch becomes hydrated, and furthermore has its cellulose cap- 
sule removed from the granulose, both of which circumstances 
make it much more susceptible to salivary influences. 

However, it must be admitted that the practical effect of pty- 
alin in digestion is not very considerable, mainly because the 
food is not kept in the mouth long enough. Although large 
quantities of saliva are swallowed with the food, its action in the 
stomach is inhibited by the acidity of the gastric juice. The 
conversion of starch into sugar is continued and concluded in 



DEGLUTITION. 95 

the small intestine. It therefore follows that the chief value of 
the saliva is in the mechanical function already referred to. 

Deglutition. 

The act of deglutition is commonly divided into three periods, 
depending upon the part through which the food is passing. 
During the first period the bolus passes from the mouth through 
the isthmus of the fauces, during the second through the pharynx, 
and during the third through the esophagus into the stomach. 
A brief reference to the anatomy of these parts is necessary. 

Fauces. — The isthmus of the fauces is the opening at the back 
of the mouth, bounded below by the base of the tongue, above 
by the soft palate and uvula, and laterally by the pillars of the 
fauces, between which are the tonsils. The anterior pillars are 
easily seen when the mouth is opened widely, and consist of the 
palatoglossi muscles with their covering mucous membrane. 
The posterior pillars approach each other more nearly than the 
anterior, and consist of the palatopharyngei muscles and their 
covering mucous membrane. 

Pharynx. — The pharynx extends from the basilar process of 
the occipital bone above about four and a half inches downward. 
It communicates with the posterior nares, the mouth, the Eus- 
tachian tubes, the larynx and esophagus. The tube is made up 
of two coats, an external muscular and an internal mucous. The 
muscular coat consists of the three constrictors and the stylo- 
pharyngeus. The mucous coat is covered in its upper part with 
columnar ciliated and in its lower part by pavement epithelium. 

Esophagus. — The esophagus runs a course of about nine 
inches from the end of the pharynx, at a point behind the cri- 
coid cartilage, to the stomach, which it enters a little to the 
left of the median line. The coats of the esophagus are two, 
an external muscular and an internal mucous. The external 
coat has its fibers disposed in two layers, longitudinal and cir- 
cular. The circular layer is internal. In the upper third of the 



96 DIGESTION. 

esophagus the fibers of the muscular coat are all striped, but at 
the beginning of the middle third they begin to give place to 
plain fibers, and these latter progressively increase, to consti- 
tute virtually the whole muscular coat at the diaphragm. The 
internal mucous coat is lined by squamous epithelium, and, 
except during the passage of substances through the esophagus, 
is thrown into longitudinal folds. The outside fibrous tissue 
which attaches the whole esophagus to the surrounding tissue 
need not be considered as a proper coat of that organ. 

Mechanism of Deglutition. — The first period of deglutition 
is voluntary but automatic, like respiration. The morsel of food 
is forced toward and through the fauces by the tongue, which 
presses from before backward against the hard palate, with the 
bolus above it. That the tongue is mainly concerned in this 
act is shown by inability to swallow when this organ is absent, 
unless the food be pushed far back into the mouth by the finger 
or other means. 

The mechanism of the second period is much more complex. 
The food must pass through the pharynx into the esophagus, 
and must not be allowed to enter any of the other openings 
communicating with the pharynx. The larynx especially is to 
be protected. Since the air enters through the posterior nares 
above the isthmus and must enter the larynx in front of the esoph- 
agus, it follows that the current of air would cross the current 
of food if swallowing and respiration took place together. Con- 
sequently respiration is suspended during deglutition. As soon 
as the food has passed the fauces, the elevators of the hyoid raise 
that bone, and with it the larynx. It is at the same time pulled 
a little forward, and since the pharynx is attached to the larynx 
posteriorly, the former necessarily follows the movement of the 
latter, and is thus slipped under the base of the tongue and the 
entering bolus. With elevation of the larynx the superior 
constrictor of the pharynx contracts upon the food, and 
passes it quickly to the grasp of the middle constrictor, which 



DEGLUTITION. 97 

in turn hands it to the inferior constrictor and thence to the 
esophagus. 

The posterior nares are protected by contraction of the 
posterior pillars and the superior constrictor. The laryngeal 
opening is protected by the epiglottis. When the tongue is 
forced back and the larynx raised the natural effect would be 
to fold the epiglottis down over the laryngeal opening. At 
the same time contraction of the pharyngeal muscles draws to- 
gether the sides of the larynx and aids in closing the glottis. 
Furthermore, the vocal cords fall together (as they always lie 
except during inspiration — and inspiration is now suspended). 

The third period passes the food through the esophagus into 
the stomach by contraction from above downward of successive 
portions of its muscular wall. Contraction of the longitudinal 
fibers draws the mucous membrane above the bolus. Then the 
circular fibers, contracting in successive segments from above 
downward, force the bolus before them. These movements are 
continued until the food reaches the stomach. The time con- 
sumed in swallowing a given article is about six seconds. 

This is the mechanism which carries all materials through the 
alimentary canal from the esophagus to the anus. It is called 
peristalsis, or vermicular (worm-like) action. 

Nervous Control. — While nearly all the muscular tissue con- 
cerned in deglutition is of the striated variety, the whole proc- 
ess, except the first, which is automatic, must be considered as 
reflex. The mechanism of deglutition is one of the best ex- 
amples of finely coordinated muscular action to be found. The 
afferent fibers concerned are from the 5th, 9th and 10th, and 
the superior laryngeal branch of the last. . The efferent fibers are 
from the 5th, 7th, 9th, 10th and 12th. The center for the re- 
flex is supposed to be far forward in the medulla. 

It ought to be added that the Kronecker-Meltzer theory of 
deglutition assails with considerable plausibility the mechanism 
of deglutition as above given. In a word, this theory holds 
7 



98 DIGESTION. 

that when the bolus of food rests upon the dorsum of the tongue, 
and the tip of that organ prevents, by its apposition to the hard 
palate, the escape of the food forward, the mylohyoids contract 
with great force, compress the food, and it escapes by the route 
of least resistance, which is backward. It is thus shot into the 
esophagus, and the contraction of the pharyngeal muscles only 
supplements that of the mylohyoids. 

Gastric Digestion. 

1 
Anatomy. — The stomach is situated beneath the diaphragm 

in the upper part of the abdominal cavity, and is moored by the 
esophagus and folds of the peritoneum. Its general shape has 
been compared to that of the bagpipe. Its large, or fundic, end 
is to the left ; its small, or pyloric, to the right. By far the 
greater part of the organ is to the left of the median line. A 
very considerable portion is to the left of the esophageal open- 
ing. Except when distended, its anterior and posterior walls 
hang in an approximately vertical direction, and are usually 
in contact by their mucous surfaces. Its greatest length when 
moderately distended is about fourteen inches, its transverse di- 
ameter about five inches, and its capacity about five pints. At 
the point where the anterior and posterior walls meet inferiorly, 
the great omentum (the peritoneum from the two walls) is given 
off. This is the greater curvature and has the gastro-epiploica- 
dextra and the gastro- epiploica-sinisira arteries running along it 
between the two folds of the omentum. Where the anterior and 
posterior walls meet superiorly, the stomach is joined by the 
lesser omentum, the two layers of which are continued in 
front and behind as the serous covering of the stomach. This 
is the lesser curvature, and has the gastric and pyloric branch of 
the hepatic arteries running along it between the two layers of 
the lesser omentum. The large left hand portion of the 
stomach cavity is called the fundus or greater pouch. The op- 
posite portion of the cavity is called the lesser pouch or antrum 



GASTRIC DIGESTION. 

Fig. 26. 



99 




Human Alimentary Canal. 
a, esophagus; b, stomach; c, cardiac orifice; d, pylorus; e, small intestine; f, biliary 
duct; £-, pancreatic duct; h, ascending colon; z, trans veise colon ; j descending colon; k, 
rectum. ( Collins <5^ Rockwell. ) 

L of C. 



IOO DIGESTION. 

pylori. At one end is the cardiac or esophageal opening, at 
the other the pyloric. 

Histology. — The coats of the stomach walls are three. From 
without inward these are the (i) peritoneal, or serous, (2) mus- 
cular and (3) mucous, 

1 . The peritoneal coat covers the whole of the organ except- 
ing an inconsiderable linear area, where the two layers of the 
lesser (gastro -hepatic) omentum join it along the lesser curva- 
ture, and a similar area along the greater curvature, where the 
serous coats of the anterior and posterior walls leave the organ 
to form the great omentum. This coat is simply a fold given 
off from the peritoneum to envelop the stomach in practically 
the same manner as the other abdominal viscera. Its structure 
is that of serous membranes in general. 

2. The muscular coat, varying in thickness from -^ in. over 
the fundus to -^ in. at the pylorus, is disposed in three layers, 
(#) external longitudinal, (£) middle circular and (V) internal 
oblique. The longitudinal fibers are continued from the cor- 
responding fibers of the esophagus. They are marked along 
the lesser curvature, but not very distinct over other parts. The 
circular fibers are not abundant to the left of the esophageal 
opening. They progressively increase toward the right, and at 
the pyloric opening constitute a distinct and powerful muscular 
ring, the pyloric sphincter, which, projecting into the lumen, 
presents a more or less flat surface on the duodenal side to pre- 
vent the regurgitation of food. The oblique fibers are supposed 
to be continuous with the circular fibers of the esophagus. 
They extend over the greater pouch from a point just to the left 
of the esophageal opening to a point on the greater curvature, 
about the junction of the middle and pyloric thirds. Here, at 
the right hand limit of the oblique fibers, the stomach is said 
during digestion to be considerably constricted, so that a tem- 
porary sphincter is established. This point is the point of 
separation between the fundus and the antrum pylori, and is 






STRUCTURE OF THE STOMACH. 



IOI 



sometimes called the sphincter antri pylorici. The fibers of 
the muscular coat are of the plain variety, as is all the gastro- 
intestinal muscular tissue from the lower end of the esophagus 

to the external sphincter. 

Fig. 27. 

E 




Serosa. — ^ 

V. S. Wall of Human Stomach. 
is, epithelium ; G, glands; Mm, muscularis mucosae. X 15. {Stirling.) 

3. The mucous coat has an average thickness of about J T 
in., is loosely attached to the muscular coat, and, except during 
gastric digestion, is thrown into longitudinal rugae. It con- 
sists of columnar epithelium resting upon a basement membrane, 
beyond (underneath) which is the capillary blood supply. 
Throughout the greater part of the stomach the mucous mem- 
brane can be shown to be divided by delicate connective tissue 
into numerous polygonal depressions, from the bottom of which 



102 DIGESTION. 

extend the gastric glands. For a description of these glands 
and the general properties of the gastric juice, together with the 
mechanism of gastric secretion, see Secretion, page 60 et seq. 

Condition of Food on Entering Stomach. — The food has 
entered the stomach in the same condition in which it left the 
mouth. It has been more or less completely triturated by mas- 
tication ; the whole has been moistened, and a part dissolved 
by the saliva. All the materials taken in have been thoroughly 
mixed with each other, and some of the starch has been con- 
verted into sugar. The reaction is now alkaline, unless the 
acidity of the articles taken has been too great to be overcome 
by the alkalinity of the saliva — in which case there would be no 
amylolytic change. Excepting starch, all foods entering the 
stomach are chemically unaffected. It remains to see what hap- 
pens to the foods under the influence of gastric digestion. 
These changes are brought about by the gastric juice, aided by 
muscular movements of the stomach. 

Gastric Juice. — Gastric juice may be secured in several 
ways, but the most reliable article for experimentation is taken 
from a previously established gastric fistula in one of the lower 
animals. It is a thin, almost colorless liquid of an acid re- 
action, and a specific gravity of 1005 to 1009. Chemically it 
contains per thousand about 973 parts water and 27 solids. 
Organic substances compose some 17 of the 27 parts of solid 
matter. The organic substances are mainly mucin, pepsin and 
rennin. The most important inorganic constituent is free 
hydrochloric acid. The others are chiefly the chlorides of 
sodium, potassium, calcium, and ammonium, and the phosphates 
of iron, calcium and magnesium. Gastric juice will resist put- 
refaction for a long time, probably on account of the free acid. 
Its digestive properties are due to the proteolytic enzyme, 
pepsin, the milk-curdling enzyme rennin, and the free hydro- 
chloric acid. 

Hydrochloric Acid. — The amount of free hydrochloric acid 



GASTRIC JUICE. T03 

present in normal gastric juice is from two-tenths to three-tenths 
of one per cent. It has been frequently claimed that the acid- 
ity of this secretion is due to an organic acid, (lactic), but 
while it cannot be denied that lactic acid, from the fermentation 
of carbohydrates, is, or may be, normally in the stomach during 
digestion, yet hydrochloric acid is undoubtedly the free acid 
proper to the gastric juice. Digestion, however, will proceed 
under a proper (variable) degree of an acidity from almost any 
acid. 

Theories as to the method of production in the stomach of 
hydrochloric acid are noticed under Secretion. It is very prob- 
ably a product of the parietal cells in the so-called acid or 
fundic glands, but beyond the fact that it is manufactured from 
the neutral chlorides of the blood in the mucous membrane, 
nothing is definitely known. Beyond an insignificant effect 
in converting cane sugar into dextrose, its function is a passive 
one, namely, that of simply making the secretion acid, so that 
pepsin may act upon the proteids. 

Pepsin. —Pepsin is a proteolytic enzyme, the composition of 
which has not been determined. From the definition, it con- 
verts proteids into peptones. It operates only in an acid me- 
dium. Hence its action is contingent upon the presence of an- 
other constituent of the gastric juice, namely, hydrochloric acid. 
Pepsin is a typical enzyme, and reference to the characteristics 
of those bodies will avoid repetition of its properties here. 

Rennin. — Rennin has the property of coagulating milk. It 
acts upon the soluble proteid of milk (casein), changing it into 
an insoluble product, which is precipitated. Acids also will co- 
agulate casein. Milk standing has lactic acid produced by the 
action of bacteria upon the lactose in it, and this acid precipi- 
tates the curd. The acid of the gastric juice might be sufficient 
to bring about this result, but the quick coagulation of milk 
when it is introduced into the stomach is probably not due to 
the acid, since neutral extracts of the gastric mucous membrane 



104 DIGESTION. 

will themselves curdle milk. After coagulation the action of 
pepsin begins and the casein is converted into peptones in the 
usual manner. The value of the curdling process is not ap- 
parent. 

Action of Gastric Juice on Foods. (A) On Proteids. — A 
familiar test for the proper performance of gastric digestion is 
the observation of the effect of the juice in a given case upon 
the white of an egg (proteid). In normal gastric juice, or in a 
properly prepared artificial solution, the egg is seen to swell up 
and dissolve. This soluble proteid is now called peptone, and 
it differs from the proteid of the egg in certain important re- 
spects, to be noted later. But, although peptone is the final 
product of pepsin-hydrochloric action, there are certain sub- 
stances produced intermediate between the initial proteid and the 
final peptone, just as in case of the formation of maltose by 
ptyalin. Some of these substances have been called acid-albu- 
min, parapeptone, propeptone, etc. But whatever they may be, 
the nomenclature of Kuhne is being largely followed at present. 
He supposes that the first product is an acid-albumin which he 
calls syntonin ; that syntonin under the influence of pepsin 
undergoes hydrolysis, taking up water and splitting into primary 
proteoses ; that each of these primary proteoses takes up water 
and splits into secondary proteoses ; that these last undergo a 
similar change with the production of peptones ; so that the suc- 
cessive substances are proteid, syntonin (acid-albumin), primary 
proteoses, secondary proteoses, peptones. 

Peptones can be shown to be different from syntonin and the 
proteoses by chemical reactions. The chief object of proteo- 
lytic digestion is to get the proteids into a diffusible condition. 
Peptones differ from proteids in at least three important respects : 
(i) They can pass through animal membranes, that is, can be 
absorbed; (2) they are no longer coagulable by heat or many 
acids ; (3) they are capable of assimilation by the cells after they 
have been absorbed. 



EFFECTS OF GASTRIC JUICE. 105 

(£) On Carbohydrates, — There is no enzyme furnished by 
the stomach to affect any of the carbohydrates. It is true 
that salivary digestion proceeds in some small degree in the 
stomach. Saliva is swallowed with the food, and until the re- 
action becomes acid (which cannot be immediately), there is 
no reason why the conversion of starch into maltose should not 
proceed. It is also true that the mere acid of the gastric juice 
can slowly convert cane sugar into dextrose. Simple acidulated 
water will do the same. 

( C ) On Fats. — Neither is there any fat -splitting enzyme in the 
gastric secretion. So far as any chemical change is concerned, 
the fats leave the pylorus in exactly the same condition as they 
entered the mouth. Their physical condition, however, under- 
goes some change in the stomach. The body temperature is 
sufficient to liquefy them, the vesicles in which the droplets are 
contained are dissolved, and, thus set free, they become a part 
of the mechanical mixture, chyme, and are made easier subjects 
of intestinal digestion. 

(Z>) On Albuminoids. — The albuminoids are acted upon by 
pepsin and hydrochloric acid in much the same way as are the 
proteids. Taking gelatin as a type, gelatoses are formed instead 
of proteoses. It is stated that peptic digestion does not go fur- 
ther than the gelatose stage with the albuminoids, conversion 
into peptones taking place under the influence of trypsin. 

Resistance of Stomach Wall to Digestion. — It would be in- 
teresting to know why the stomach (or the intestine) does not 
digest itself. If a portion of the stomach of another animal be 
placed in that of a living animal, it will be digested ; or if the 
circulation be cut off from a limited area of the stomach, the 
secretion will frequently digest that part of the organ and 
bring about a perforation ; or further, if any living part of an 
animal, as the leg of a frog, be fastened in the stomach of an- 
other animal, it will likewise be digested. The last instance 
would seem to lead to the conclusion that living matter can be 



Io6 DIGESTION. 

digested, but in reality it is shown (Bernard) that the tissue is 
first killed by the acid, and that no digestion takes place in the 
alkaline intestinal juice. But why the stomach is not thus at- 
tacked when other living tissue is remains obscure. The most 
plausible theory is that the gastric epithelium is possessed of 
some power, mechanical or physical, the nature of which is un- 
known, inhibiting the action of the gastric juice, most probably 
by preve?iting its absorption. 

This theory, it should be said, simply represents an advance 
in our probable knowledge of the subject, and does not claim 
to be an explanation of the phenomenon. 

Movements of the Stomach. — Whether the exact details of the 
muscular movements of the stomach be known or not, the essential 
fact to be remembered is that the organ is in a more or less con- 
tinuous state of muscular activity for several hours after the 
ingestion of an ordinary meal, and that this activity results in the 
physical disintegration of most of the solids introduced, in the 
thorough mixing of all the classes of foods with each other and 
with the gastric juice, and in the passage from time to time of 
such parts as have been reduced to a pultaceous condition through 
the pylorus into the duodenum, until finally the stomach is 
empty. 

In considering the mechanism of these movements a division 
of the organ into two segments, fundic and pyloric, by the 
sphincter antri pylorici is to be kept in mind. When food has 
entered the stomach the peristaltic wave of contraction begins 
at the splenic end and passes toward the right. This contraction 
is comparatively weak, is mainly evident along the greater 
curvature, and increases in strength as it passes toward the 
pylorus. Its wave-like character is due to the contraction and 
subsequent relaxation of successive bands of circular and oblique 
fibers. Regurgitation of food is prevented by a rhythmical 
contraction of the lower end of the esophagus, and the effect 
of this muscular wave (peristalsis) in the fundus is to force the 



MOVEMENTS OF THE STOMACH. I07 

food toward the pylorus. But when the right end is reached, 
the rather firm contraction of the sphincter antri pylorici pre- 
vents the entrance into the antrum of all except the liquid or 
semi -liquid parts. The food, thus denied admission to the 
antrum, takes a course along the lesser curvature to the splenic 
end, then back along the greater curvature, and such parts of 
it as have, during this revolution, been sufficiently dissolved 
pass into the antrum. These revolutions continue until the 
fundus has been emptied. 

It is not to be supposed that food has been accumulating 
meantime in the antrum. Indeed, it is certain that muscular 
contractions are here much more active than in the fundus, 
where the movements are slow and of a rather compressing nature. 
It is thought that very soon after the entrance of food from the 
fundus the entire muscular wall of the antrum undergoes very 
strong contraction of a peristaltic (possibly systolic) nature, 
and the pultaceous parts of its contents are sent with some force 
into the duodenum. Those which are not sufficiently dissolved 
to pass the pyloric sphincter are said to excite an anti -peristaltic 
movement, whereby they are thrown back into the fundus for 
further digestion— the sphincter antri pylorici having now relaxed. 
However, substances which the gastric juice and contractions 
cannot dissolve will finally pass the pylorus, but they are prob- 
ably delayed for a considerable time. 

This succession of movements is continued with a rapidity 
and regularity varying with the condition of the organ and the 
nature of its contents. They last until the organ is emptied 
in part by the absorption of its contents, but mainly by their 
passage into the small intestine. Each circuit in the fundus 
probably occupies about three minutes, and gastric digestion as 
a whole lasts usually from two to five hours. The contraction 
and relaxation of plain muscle is much slower than that of 
striped. 

It is the fundus, and not the pylorus, which serves as a 



Io8 DIGESTION. 

reservoir and in which the greater part of gastric digestion 
occurs. The precise condition of the pyloric sphincter during 
gastric digestion is unknown. It may have simply an exalted 
degree of tonicity which does not completely close the opening 
and which can be overcome by pressure, or it may be tightly 
contracted and require a distinct nervous dispensation to effect 
its relaxation for the passage of fluids as well as solids. It 
would seem that the length of time for which food is detained 
in the stomach depends more upon its physical condition than 
upon its chemical — that is, than upon any stage of digestion 
which it may have reached ; for it can be shown that fluids pass 
very quickly into the intestine. 

The secretory occurrences during these movements are of the 
greatest importance (see p. 60). 

Nerve Supply. — The stomach is supplied with pneumogastric 
and sympathetic fibers. These latter can be traced through the 
solar plexus, splanchnics and cervical ganglia to the spinal cord. 
They exert an inhibitory effect on the muscular tissues ; their 
stimulation causes relaxation. The vagus fibers are motor ; their 
stimulation causes contraction. But these nerves serve only to 
regulate the muscular movements. It is the stimulus of food in 
the stomach which excites gastric peristalsis. It is not stopped 
by section of these nerves, though it may be interfered with. 
This stimulation is exerted either directly upon the nerve fibers 
or upon the ganglia of the stomach wall. 

The conditions influencing gastric digestion operate mainly 
through changes in the quality and quantity of gastric juice. 
For mention of some of these, together with the nerves con- 
trolling gastric secretion, see article on Secretion. 

Resume of Gastric Digestion. — The condition, physical and 
chemical, of food entering the stomach has been mentioned. 
Before leaving it the mass has been thoroughly mixed with 
gastric juice which, aided by the movements of the stomach, has 
softened and disintegrated and made of it a semi-fluid mechan- 



INTESTINAL DIGESTION. 109 

ical mixture, chyme. Some of the proteids and albuminoids 
have been converted into peptones. The carbohydrates have 
been unaffected, except so far as ( i ) the action of the swallowed 
saliva has continued slightly upon the starch and (2) the acid 
juice has converted a little cane sugar into dextrose. The fats 
are likewise unaffected, except to have the globules set free and 
dissolved and made a part of the general mixture. This, then, 
is the mass which passes, largely undigested, into the duodenum. 

Intestinal Digestion. 

Anatomy. — The small intestine extends from the pylorus to 
the caput coli, and is about twenty feet in length. It lies in 
numerous coils which are held loosely in place by a fold of 
peritoneum running from one side of the great abdominal ves- 
sels, enveloping the gut, and returning to the parietal wall on 
the opposite side of the vessels. The fold thus attaching the 
intestine to the abdominal wall is the mesentery. The distance 
along the mesentery from this parietal region to the gut is three 
or four inches, except at the beginning and end of the small 
intestine, where it is shorter, to bind the tube more firmly in 
place. The upper eight or ten inches of the small gut is called 
the duodenum, the next eight feet the jejunum, and the re- 
mainder the ileum. No anatomical peculiarity separates these 
parts. Their average diameter is about one and a quarter 
inches. 

Histology. — The wall of the intestine is in three layers, ex- 
ternal or serous, middle or muscular and internal or mucous. 

The external layer consists of the enveloping fold of peri- 
toneum and needs no description, except that, like serous mem- 
branes elsewhere, it furnishes a lubricating secretion to provide 
for the easy gliding of the intestines over each other and over 
the other viscera. The middle coat has its muscular fibers dis- 
posed in two layers, an external longitudinal and an internal 
circular. The latter is the stronger. Between the two mus- 



no 



DIGESTION. 



cular layers is the nervous plexus of Auerbach ; between the 
circular layer and the mucous coat is that of Meissner. These 
communicate with each other by fibers of extension. The in- 
ternal mucous coat presents several points deserving mention. 




Diagram of a Longitudinal Section of the Wall of the Small Intestine. 

a, villi; b, Lieberkuhn's glands; c, tunica muscularis mucosae, below which lies Meissner's 
nerve plexus ; d, connective tissue in which many blood and lymph vessels lie ; e, circular 
muscle fibers cut across with Auerbach's nerve plexus, below it ; f, longitudinal muscle 
fibers; g, serous coat. {Yeo.) 

These are (i) valvule conniventes; (2) villi; (3) secreting 
glands, (a) of Brunner and (<£) of Lieberkuhn ; (4) solitary 
and agminate glands. 

1. The valvulae conniventes are simply transverse folds or 
tucks of the entire mucous membrane, each of which extends 
from one -third to one -half around the circumference of the tube 
and projects by its middle portion sometimes to the center of the 
lumen. These small folds, 800 to 1000 in number, extend from 
about the middle of the duodenum to the beginning of the last 
third of the ileum and greatly increase the length of the mucous 
membrane over that of the gut proper. They are not effaced 
by the passage of food or by other circumstances, for the two sur- 
faces of the fold which are in apposition are bound together by 
loose connective tissue. The fold as a whole, however, is 



VILLI. 



Ill 



freely movable upward or downward in the intestine and has no 
tendency to obstruct the canal. The only function of the val- 
vulae conniventes is to furnish a greater secreting surface and, 

Fig. 29. 




Portion of the Wall of the Small Intestines laid open to show the Valvule 
Conniventes. (From Yeo after Brinton.) 

by somewhat retarding the passage of the alimentary mass, to 
subject it for a longer time to the digestive fluids. 

2. The villi are especially important in connection with ab- 
sorption, and their description properly belongs under that 
head. They are conical elevations responsible for the velvety 

Fig. 30. 




Vertical Section of a Villus of the Small Intestines of a Cat. 
a, striated border of the epithelium ; b, columnar epithelium ; c, goblet cells ; d, central 
lymph-vessel; e, smooth muscular fibers; f y adenoid stroma of the villus in which lymph 
corpuscles lie. {Kirkes after Klein.) 



112 DIGESTION. 

character of the mucous membrane. They exist in great num- 
bers from the pylorus to the ileo -cecal valve, covering the 
valvulae conniventes as well as the general surface of the mucous 
membrane. The largest are about -^ in. long and -^ in. in 
diameter at their base. They are only elevations of the mucous 
membrane containing a central tube, the lacteal, which is 
nothing but an intestinal lymphatic. The structure from without 
inward — that is, from the surface of the villus inward to its 
center — is (i) a layer of columnar epithelium resting upon a 
delicate basement membrane; (2) lymphoid tissue containing 
abundant capillaries and connective tissue cells; (3) a thin 
layer of plain muscle fibers continuous from the intestinal wall ; 
(4) the lacteal, whose endothelial wall contains many stomata. 

3. The glands of Brunner and the crypts of Lieberkuhn, or 
intestinal tubules, are supposed to produce the succus entericus. 
The former are chiefly limited to the upper half of the duode- 
num. The latter exist throughout the small and large intestine. 
For further description of them see Secretion, page 65. 

4. The solitary and agminate glands are not supposed to 
contribute to the production of the intestinal juice. They are 
alike in structure, the agminate glands being only a collection 
of solitary glands. The former are the Peyer's patches, so 
important in the pathology of typhoid fever. These patches 
are usually about twenty in number and confined to the lower 
two-thirds of the ileum, where they occupy that portion of the 
circumference of the tube opposite the attachment of the mes- 
entery. Their average dimensions are 1 x 1% in. They 
consist essentially of lymphoid tissue, the separate follicles of 
which are surrounded by lymphatics and penetrated by blood- 
vessels. They are covered by villi, but the valvulae conniventes 
cease at their edges. The solitary glands are more widely dis- 
tributed than the agminate. 

The chyme, having passed from the stomach to the small in- 
testine, encounters three digestive fluids, pancreatic juice, bile 



TRYPSIN. II3 

and intestinal juice. These are, of course, mixed together, but 
none interferes with the action of the other. 

Pancreatic Digestion. — For a description of the pancreas 
and the mechanism of its secretion see page 66. 

The pancreatic juice has an alkaline reaction, and a specific 
gravity of about 1040. It quickly undergoes putrefaction, and 
coagulates if heated. Taken from a recent fistula, it contains 
of water about 900 parts per 1000 and about 100 parts solids. 
Organic substances constitute the main part of the solids. 
The salts are the phosphates of sodium, calcium and magnesium, 
the chloride and carbonate of sodium. The important organic 
substances are the enzymes, trypsin, amylopsin and steapsin. 
The pancreatic juice is very comprehensive in its digestive 
properties — more so than any of the other secretions. Some 
claim that it also contains rennin. 

Trypsin. — Trypsin, like pepsin, converts proteids into pep- 
tones. Nothing positive is known of its composition, but it is 
possessed of the usual characteristics of enzymes regarding tem- 
perature, etc. It differs from pepsin in that its proteolytic 
action is more powerful and can take place in alkaline media. 
It will also act in neutral or weakly acid media. The opinion 
is advanced that while the gastric juice is capable of converting 
proteids into peptones, as a matter of fact it does not usually 
carry the process further than the proteose stage, and thus 
prepares the proteoses for tryptic digestion. 

It was seen that the successive products of pepsin-hydrochloric 
digestion are syntonin, primary proteoses, secondary proteoses 
and peptones. In tryptic digestion it seems that, in the split- 
ting process, the syntonin (here alkali-albumin) and primary 
proteose stages are omitted, and the first product is secondary 
proteoses, which are split into peptones. Furthermore, trypsin 
goes a step beyond with some of the peptones and converts them 
into simpler compounds, the best known of which are leucin and 
tyrosin. These are found normally in the intestinal canal, but 



114 DIGESTION. 

the physiological importance of this conversion is not apparent. 
The opinion that it is a useless sacrifice of useful peptones does 
not seem warranted. 

Amylopsin. — The amylolytic enzyme, amylopsin, is identical 
in its action with ptyalin. For the supposed reactions taking 
place see page 93. This enzyme is very important, for it has 
been remarked that the action of ptyalin is probably rather in- 
consequential, and by far the greater portion of the starch, 
which constitutes a large part of our ordinary food, must be di- 
gested in the small intestine — and almost entirely by amylopsin. 

Steapsin. — Under the influence of steapsin neutral fats take 
up water and undergo hydrolysis, with the production of glyc- 
erin and the fatty acid corresponding to the kind of fat which 
is split up. In the intestine it is probable that only a part of 
the neutral fats are thus split into glycerin and fatty acids. The 
fatty acids thus formed unite with the alkaline salts to form 
soaps, and these soaps, aided by intestinal peristalsis, convert 
the remaining fats into an emulsion. The products of fat diges- 
tion are therefore glycerin, soaps and emulsions, all of which 
can be absorbed in a way to be noted later. While the emulsi- 
fication of fats under the influence of soaps (fatty acids and alka- 
line salts) is an undoubted effect, the method of procedure is 
unknown. It is certain that the emulsification is aided by the 
presence of bile, although this fluid possesses no fat-splitting 
enzyme. 

Bile in Digestion. — The bile is not, properly speaking, a di- 
gestive fluid, for it contains no enzyme capable of effecting di- 
gestive changes in any of the foods ; but it so materially affects 
the action of some of the other fluids that it cannot be over- 
looked in a discussion of intestinal digestion. The liver, its 
anatomy, functions, etc., are best considered elsewhere (see 
page 69, et seo.), and reference will here be made only to the 
connection of the bile with digestion. 

So far as the bile acids, glycocholic and taurocholic (com- 



SUCCUS ENTERICUS. 115 

bined to form salts of sodium) are concerned, the fluid is a se- 
cretion, and it is these which are mainly concerned in the diges- 
tive process. The production of bile is continuous, but the 
gall bladder acts as a reservoir in which a part at least of the 
secretion is stored in the intervals of digestion, to be discharged 
in greater abundance when chyme enters the duodenum. While 
the action of bile in most of the digestive functions to be men- 
tioned is obscure, it is known to have at least these uses : 

1. It promotes intestinal peristalsis. 

2. It has an inhibitory effect on putrefaction in the intestinal 
tract. By this it is not to be understood that the bile is directly 
antiseptic, for it undergoes putrefaction very readily itself, but 
only that in some way its withdrawal from the substances passing 
through the alimentary canal allows their more ready disinte- 
gration. 

3. It aids in the emulsification of fats. 

4. It promotes the absorption of fats. Recently the state- 
ment that the bile promotes all kinds of absorption has appar- 
ently been successfully disproved, but it seems certain that 
" the bile acids enable the bile to hold in solution a considerable 
quantity of fatty acids, and possibly this fact explains its connec- 
tion with fat absorption." (American Text-Book.) 

The Succus Entericus. — The intestinal secretion, or succus 
entericus, is a product of the crypts of Lieberkuhn and Brun- 
ner's glands. It is scanty, of a yellow color and an alkaline re- 
action. Opinions vary as to what foods are affected by this 
fluid, but since the more recent experiments have overcome 
some difficulties in obtaining specimens, the conclusions based 
upon them seem most reliable. It is said to have no effect on 
proteids or fats. It contains an amylolytic enzyme, which aids 
the pancreatic juice in converting starch into maltose. It also 
has an enzyme, invertase, which converts cane sugar into dex- 
trose and levulose, as well as an allied enzyme, maltase, which 
converts maltose into dextrose. The carbohydrates are absorbed 



Il6 DIGESTION. 

as dextrose, with the probable exception of lactose. It is 
mainly cane sugar, maltose (from starch) and lactose that are in 
the alimentary tract and require to be thus changed to dextrose. 

It is not out of place to say that ptyalin produces maltose and a 
little dextrose, and that the pancreatic juice and succus entericus 
produce maltose and considerable dextrose. The maltose is 
converted into dextrose during the process of absorption. It 
is, therefore, customary to say that the carbohydrates are ab- 
sorbed only as dextrose. 

Movements of the Small Intestine. — The effect of intesti- 
nal movements is to force the contents onward through the 
ileo-cecal valve. Here it is that typical peristalsis is found. 
The main factor in the passage is the layer of circular fibers. 
Contraction of these fibers in the upper duodenum may at least 
be conceived to begin upon the introduction of chyme. The 
contraction passes down the gut in a wave-like manner, the 
wave being produced by the contraction of segment after seg- 
ment of the circular fibers with relaxation just behind the ad- 
vancing contraction. The tendency of such a movement is to 
force the alimentary mass along the canal. The longitudinal 
fibers are probably chiefly concerned in changing the position of 
the intestine and in shortening the tube, and thus slipping the 
mucous membrane above the bolus, so that it can be grasped by 
the circular fibers. A continuation and repetition of these 
movements, which are slow, gentle and gradual in character, is 
finally effectual in passing the contents into the colon. It is 
not probable that anti-peristaltic movements take place normally. 

Nerve Supply. — Very probably the intestinal movements are 
naturally excited by the food and by the bile. It is probable 
also that these stimuli exert their influence through the ganglia 
of the plexuses of Auerbach and Meissner. The intestine re- 
ceives fibers from the right vagus and the sympathetic. The 
former are probably motor (contractors) and the latter inhibi- 
tory (dilators). Here, as in the stomach, they are probably 



LARGE INTESTINE. 117 

only regulators of the movements, without being actually neces- 
sary to peristalsis. 

Large Intestine. 

Anatomy. — The large intestine, known as the colon, is about 
five feet in length and is divided into ascending, transverse and 
descending portions. (See Fig. 26.) The sigmoid flexure is 
the terminal extremity of the descending colon and empties 
into the rectum. The small intestine communicates with the 
colon at right angles a little above the beginning of the latter, 
leaving below the opening a blind pouch, the cecum, or caput 
coli. From the posterior and inner aspect of the cecum runs 
off the appendix vermiformis. The diameter of the colon 
gradually decreases from two and a half to three and a half 
inches in the cecum to the beginning of the rectum. The as- 
cending colon passes upward from its beginning in the right 
iliac fossa to the under surface of the liver, where it bends upon 
itself almost at a right angle (hepatic flexure). The transverse 
colon runs directly across the upper part of the abdominal cav- 
ity to the lower border of the spleen, where an abrupt turn 
downward (splenic flexure) begins the descending colon. The 
lower part of the descending colon occupies the left iliac fossa 
in the shape of the letter S, and is the sigmoid flexure. 

The rectum, which receives the contents of the sigmoid, is 
not straight, as its name indicates. It curves (1) to the right 
to reach the median line, (2) forward to follow the contour of 
the sacrum, and (3) backward in the last inch of its course. 
It has the shape of a dilated pouch, its lower termination at the 
anus being guarded by the powerful external sphincter of stri- 
ated muscle. Its diameter is greatest below. 

The vermiform appendix has the three coats common to the 
intestine, but its muscular coat is ill-developed. The peritoneal 
coat generally forms a short meso-appendix at the root of the 
organ. The blood supply of the organ is not abundant. It is 
greater in the female than in the male, a part of it coming 



Il8 DIGESTION. 

through the appendiculo-ovarian ligament. The appendix has 
no function. 

The ileo-cecal valve, guarding the opening between the 
large and small intestines, is made of two folds, upper and 
lower, of the muscular and mucous coats, which folds project 
into the large intestine. The serous coat runs directly over 
from the small to the large intestine at their point of junction, 
without being folded inward upon itself, as are the others. This 
prevents obliteration of the folds by distention. By this ar- 
rangement the two portions of the gut communicate only by a 
buttonhole slit, which is easily opened by pressure from the di- 
rection of the ileum, but which pressure from the cecum tends 
to close more firmly. (See Fig. 26.) 

Structure. — The large intestine has the three usual coats. 
The peritoneal, however, is lacking on the posterior part of the 
cecum, ascending and descending colons, these parts being 
bound down closely and having no meso-colon. The sigmoid 
is entirely covered, as is the upper third of the rectum. The 
middle third of the rectum has no serous coat behind, being 
firmly held in place, while the lower third lacks this coat en- 
tirely. The muscular coat is peculiar, in that its longitudinal 
fibers are collected into three quite strong bands, evident to the 
eye. When the rectum is reached they spread out over the 
whole circumference of that part of the canal. These bands are 
shorter, as it were, than the wall proper, and the consequence is 
that the whole length of the large intestine is gathered up into 
a number of pouches. The mucous coat is paler than that of 
the small intestine, presents no villi and is rather closely 
adherent to the subjacent parts. In it are found glands corre- 
sponding in appearance to the crypts of Lieberkuhn, and they 
are so classed ; but they probably secrete mucus only. Some 
solitary lymphoid follicles also usually exist here. 

Changes Taking Place in the Alimentary Mass in the 
Large Intestine. — Most of the substances which enter the large 



BACTERIA IN DIGESTION. 119 

intestine have resisted the action of the various digestive fluids 
and are on their way to be discharged in defecation. Doubtless, 
though, some materials undergo digestive changes in the colon, 
not under the influence of any secretion there formed, but of 
the intestinal juice with which they are incorporated on leaving 
the ileum. The secretion of the mucous membrane of the large 
intestine furnishes no digestive enzyme, and the changes going 
on in the alimentary mass (now feces) are chiefly due to ab- 
sorption. By some unknown process, however, rectal aliments 
of an easily digestible nature are absorbed, and that in a nutritive 
form. The consistence of the fecal matter increases in its pas- 
sage through the colon, owing to the absorption of its more 
fluid portions. The bile pigment is responsible for the char- 
acteristic color. The odor is mainly due to bacterial decomposi- 
tion, but partly to the secretion of the mucous membrane. 

Bacteria in Intestinal Digestion. — The entrance of the bile 
and pancreatic juice into the duodenum changes to alkaline 
the previously acid reaction of the chyme. But it is found that, 
when an ordinary mixed diet is given, the mass leaving the ileo- 
cecal valve has an acid (organic) reaction, and that the pro- 
teids have not undergone putrefaction. The alkaline medium 
of the upper intestine favors bacterial activity, and it would 
seem that proteid putrefaction would ensue. But it is supposed 
that in health these bacteria set up fermentative changes in the 
carbohydrates, with the production of organic acids which in- 
hibit proteid putrefaction, and account for the acid reaction at 
the ileo -cecal valve. When the mass has entered the colon the 
acidity is soon overcome and putrefaction is the usual consequence. 
It can be seen how readily this delicately adjusted balance may 
be disturbed by errors in the proper kind and proportion of food, 
etc. Some of the products of bacterial activity upon carbo- 
hydrates and proteids are leucin, tyrosin, indol, skatol, phenol, 
lactic and butyric acid. The object of the production of these 
substances is unknown. 



T20 DIGESTION. 

Composition of Feces. — It seems at present that the main 
bulk of fecal matter is made up of substances which are contained 
in the intestinal secretions, and the alimentary canal is more im- 
portant in excretion than was formerly supposed. These sub- 
stances are waste matters from tissue metabolism. Besides these 
materials, the feces normally contain indigestible and undi- 
gested matters, inorganic salts, stercorin, mucus, epithelium 
from the intestinal wall, coloring matter and substances result- 
ing from bacterial activity. Stercorin is the converted form of 
cholesterin, a constituent of the bile. The coloring matter is 
from the pigment {bilirubin) of the same fluid. Of the bac- 
terial products the most important are indol and skatol. They 
represent proteid putrefaction ; they are responsible for the fecal 
odor \ hence the characteristic difference in the odor of the con- 
tents of the ileum and colon. The reaction of fecal matter 
varies. The amount for the average person is about four and a 
half ounces per day. 

Gases. — Hydrogen, nitrogen and carbon dioxide are found 
normally in the small intestines. They serve to keep the tube 
patulous, and avoid obstruction, and also to prevent concussion. 
In the large intestine bacterial activity increases the number of 
gases present. Here, in addition to those found in the small 
intestine, there are carburetted and sulphuretted hydrogen, with 
others at times. 

Movements of the Large Intestine. — The muscular contrac- 
tions of the colon forcing the feces onward are of the same 
general character as those of the small intestine, though less 
violent. The contents thus passed analward by peristalsis 
accumulate gradually in the sigmoid flexure until defecation 
occurs. 

Defecation. — The act of defecation is both voluntary and in- 
voluntary \ — -voluntary in the relaxation of the external sphincter 
and involuntary in the peristalsis which brings the fecal matter 
to present at that muscle. It is probable that the rectal pouch 



DEFECATION. 12 1 

does not usually contain feces, but that the desire to defecate is 
brought about by the entrance of the mass into it from the sig- 
moid. Then, if the desire be obeyed, peristalsis of the non- 
striated muscular coat continues, the internal sphincter of plain 
muscle relaxes, as does also the external of striped muscle, and 
evacuation takes place. 

Usually, by an effort of the will, evacuation can be voluntarily 
prevented by maintaining the tonic contraction of the external 
sphincter. If the desire to defecate be disregarded, the fecal 
accumulation probably returns to the sigmoid, leaving the rec- 
tum comparatively empty. The act of evacuation is commonly 
aided further by voluntary contraction of the diaphragm and 
abdominal muscles. The lungs are filled, " the breath is held ' ' 
(forcing down and holding the diaphragm), and the abdominal 
muscles likewise contract powerfully to compress the viscera and 
force the feces into the rectum. Pressure on the afferent nerves 
of the rectum probably sets up the desire to defecate, and the 
contraction of its walls, as well as the relaxation of the internal 
sphincter, is a reflex act. The center is in the lower segment 
of the cord, but it is connected with the cerebrum, as is shown 
by emotional influences on the act. 

The average time occupied in the passage of the residue of an 
ordinary meal from the mouth to the rectum is about 24 hours. 
Something like 12 hours of this is thought to be spent in the 
large intestine. 

While it has been endeavored to establish clearly the separate 
action of each fluid with which the aliment comes in contact, it 
is to be remembered that they form a mixture, the combined 
activity of whose component parts results in the extraction of 
all the nutritive material from the bolus in its long journey 
through the gastro -intestinal tract. It can hardly be said to be 
still at any time during that passage, the continual peristalsis to 
which it is subjected facilitating both the chemical action of the 
enzymes and the physical phenomenon of absorption. 



122 ■ ABSORPTION. 

Resume of Digestion. — Digestion is a chemical process, 
whereby the different classes of foods are changed so as to 
become capable of absorption and assimilation. (i) The 
i?iorganic foods are not digested, but are simply dissolved and 
absorbed. (2) The proteids and albuminoids are digested in 
the stomach by pepsin-hydrochloric acid and in the small 
intestine by trypsin of the pancreatic juice. (3) The starchy 
carbohydrates are digested in the mouth by ptyalin, whose 
action is continued slightly in the stomach, and in the small 
intestine by amylopsin of the pancreatic juice. The sugar car- 
bohydrates are digested slightly perhaps in the stomach by 
hydrochloric acid, and in the small intestine by invertase and 
maltase of the succus entericus. (4) The fats are digested in 
the upper small intestine by steapsin of the pancreatic juice, 
aided by the bile. Digestion is usually completed in the small 
intestine, but may be continued in the colon by the passage 
into it of undigested particles with the intestinal secretions. 
All the digestive secretions are alkaline in reaction except the 
gastric juice. 

It remains to be seen how these various foods find exit from 
the alimentary canal to be appropriated by the cells. It may be 
said in a general way that they are absorbed as soon as they are 
digested, and therefore from that part of the alimentary canal 
in which they undergo this change. 

(C) ABSORPTION. 

Obviously digested materials are of no service in the vital 
economy until they are absorbed — first by the circulation and 
then by the tissues themselves. Here we will consider only 
their absorption from the alimentary canal, which process, in 
contradistinction to the other, may be termed external absorp- 
tion. 

While it is known that the laws of diffusion and osmosis out- 
side the body are largely responsible for absorption within the 



OSMOSIS. I23 

organism, there are many phenomena in connection with that 
process which cannot be explained under these laws, and which 
are indeed, in some cases, at variance with them. The only 
explanation at present to be offered of anomalous action is to 
refer it to some peculiar property inherent in the cells them- 
selves — the epithelium in case of the alimentary canal. So 
profoundly important in connection with physiological activity 
are the laws of osmosis outside of the body, and what is known 
concerning the mutability of those laws inside the body, that a 
brief consideration of the subject seems necessary to an intelli- 
gent conception of many vital phenomena. 

Osmosis. — When two different kinds of gases are brought in 
contact they mingle with each other, making a homogeneous 
mixture. This is due to the continual motion of their molecules. 
When two different kinds of liquids are brought in contact, a 
homogeneous mixture results for the same reason — unless the 
liquids be non-miscible, as oil and water. If now the liquids 
happen to be separated by a membrane permeable by both, the 
result, while it may be delayed, will be the same. If, further, 
these liquids hold in solution substances the molecules of which 
can penetrate the interposed membrane, there will likewise be 
an interchange of these substances, and the fluids on both sides 
will come ultimately to have the same composition. This pas- 
sage of liquids and dissolved matters through an animal mem- 
brane is known as osmosis. 

It must be remembered that in the body particularly the inter- 
posed membrane may be permeable to the solvent, water, and less 
so, or not at all, to the dissolved substances. Materials which 
will in solution pass through a membrane are called crystalloids ; 
those which will not, colloids. If simple water be on both sides 
of the membrane, the interchange continues because of incessant 
molecular motion ; but the currents equalize each other, and no 
alteration in volume or composition becomes apparent. But if to 
the water on one side there be added a solution of some crystal- 



124 ABSORPTION. 

loid, as sugar, the excess of water will pass to that side. The 
crystalloid in solution is said to exert an osmotic ftresstire, and 
that pressure depends upon the density of the solution. In course 
of time, however, the crystalloid passing itself through the mem- 
brane, conditions of equal volume and density will be established 
on the two sides of the membrane, and osmosis in either direction 
will cease to be apparent. But if the membrane be non-permeable 
to the dissolved substance, an excess of water will pass to the 
colloid side and will continue so to pass until finally it will be 
inhibited by hydrostatic pressure on that side. This is taken as 
the measure of osmotic pressure for the colloid. 

All substances in solution, whether crystalloids or colloids, 
exert a certain osmotic pressure ; that is, they may be said to 
interfere with the passage of a current from their side of the 
membrane, and that interference depends on the number of 
molecules in solution, or, in other words, upon the density of 
the fluid. A fanciful but striking illustration refers the explana- 
tion to the continual molecular motion : the molecules of the 
dissolved substance act as a screen to protect the membrane from 
the water molecules, which are incessantly moving against it, 
and consequently, in a given time, more molecules of water will 
strike and pass through the membrane on the unscreened than 
upon the partially screened side. Evidently the number of 
molecules in solution (the density) has a material influence upon 
the escape of water from that side. Of course, since a crystal- 
loid finally passes to the less dense side in sufficient quantity to 
establish an equilibrium, the effect of its osmotic pressure is only 
temporary ; but while the osmotic pressure of a colloid may be 
less than that of a crystalloid, its effect is inclined to be perma- 
nent. For instance, if a hypertonic solution (one whose density 
is greater than that of blood serum) of sodium chloride be in- 
jected into the blood, the first effect is to cause an increased flow 
of water to the vessels, but soon enough sodium chloride passes 
out by osmosis to raise the density of the extra-vascular fluids, 



OSMOSIS. 125 

and thus to cause an escape of water from the vessels. On the 
other hand, the osmotic pressure exerted by the proteids of the 
blood is comparatively small. But since they are here chiefly as 
colloids and tend to maintain the concentration of the circu- 
lating fluid, their effect is a permanent factor influencing absorp- 
tion into the blood-vessels. 

Isotonic and hypotonic solutions are those having equal and less 
densities respectively as compared to blood serum. Hypotonic 
solutions are most easily absorbed ; hypertonic least easily. 
Application of these principles explains the rationale of giving 
some medicines in dilute and others in concentrated form. As 
to the direction of the current, the one of greater volume may 
be called the endosmotic and the one of lesser volume the exos- 
motic. For example, the current in ordinary absorption from 
the alimentary canal is usually termed endosmotic, though it 
may be reversed, as when magnesium sulphate is given. 

When it is said that the greater current is from the less dense 
to the more dense fluid, no reference is had to the direction of 
the solids in solution. If there be only one solid concerned, it 
will be the one responsible for the difference in density, and, 
if it be a crystalloid, it will pass through the membrane until 
the density on the two sides is equal, and its direction will be 
opposite to that of the water. If on the side of less density 
there be another crystalloid in solution, but in less quantity than 
the solid on the side of greater density, it will pass in the di- 
rection of the greater current of water until conditions of equal 
concentration with respect to this solid are established. In the 
laboratory the final result in any case of dissolved crystalloid or 
crystalloids is two liquids absolutely identical in composition. 
A rectal enema, hypertonic with sodium chloride, will give up 
sodium chloride to the blood, but it may at the same time draw 
upon that fluid for urea, for example. This is suggestive when 
an attempt is made to explain the products of glandular secre- 
tion, excretion, etc. It may be that the capillary walls are 



126 ABSORPTION. 

permeable to certain substances in certain situations and not in 
others. 

In the body it may be said that well nigh all the vital func- 
tions are dependent upon osmosis. There are fluids separated 
by animal membranes everywhere. In the alimentary canal, 
for instance, is a fluid containing matters fit to be absorbed \ 
ramifying in the wall of that canal are blood and lymph capil- 
laries filled with fluid ; while separating the two is an animal 
membrane consisting of the alimentary epithelium, a little con- 
nective tissue and the endothelial lining of the capillaries. 
These are conditions most favorable for osmosis, but the osmotic 
laws of the laboratory are by no means immutable in the body. 

From what has been said of osmosis in general, and consider- 
ing variations due to conditions of circulation, etc., the follow- 
ing facts seem clear as to absorption in the body : ( i ) The 
substance must be in a liquid or gaseous state • (2) it must be 
diffusible; (3) the membrane must be permeable; (4) the 
greater current is toward the more dense solution ; (5) the less 
dense the solution the more quickly will it be absorbed ; (6) 
the greater the pressure in the vessels the less rapid will absorp- 
tion into them take place; (7) absorption is more rapid the 
more rapid the blood current (continually preventing " satu- 
ration " of the adjacent blood) ; (8) the higher the temperature 
the more rapid is absorption ; (9) the " vital condition" of 
the cells is the most important factor of all. 

A thorough grasp of these principles and probabilities will do 
much to clarify almost all the phenomena of vital activity, and 
many questions of a pathological nature. 

Absorption from the Alimentary Canal. — It has been said 
that all digested materials must find their way into the blood, 
It is to be remembered that there are two ways by which they 
reach the vascular circulation : first, by direct absorption into 
the capillaries of this system, and second, indirectly, by absorp- 
tion into the lymphatic circulation and passage thence to the 



ABSORPTION FROM DIFFERENT REGIONS. 1 27 

left subclavian vein. Those lymph capillaries which are con- 
cerned in this absorption occupy the villi, and are called lac- 
teals. 

(A) From the Stomach. — Since all classes of foods except fats 
have been partly digested in the stomach, it follows that all ex- 
cept fats may be absorbed here. However, as a matter of ob- 
servation, the stomach is of much less importance in absorption 
than was once thought. Practically, it is found that water and 
salts are passed quickly on toward the duodenum and are not 
largely absorbed in the stomach. Sugar and peptones are also 
found to be absorbed rather sparingly here. All these sub- 
stances can undoubtedly be absorbed by the gastric mu- 
cous membrane, and their complete absorption is prevented 
only by their removal through the pylorus. It is interesting to 
note that alcohol and condiments, like pepper and mustard, 
greatly hasten absorption, either by increasing the blood flow or 
by directly stimulating the "vital activity" of the epithelium. 

(i?) From the Small Intestine. — Here absorption of all 
classes of food is possible, and here in fact most of the foods are 
absorbed. The digestive influences are more active upon all the 
aliments, the mucous membrane is well adapted to absorption 
by reason of its valvulae conniventes and its villi, and the food 
necessarily remains in the small intestine for a considerable 
time. The fats are absorbed in the upper part of the small in- 
testine ; for they pass into the lacteals of the villi, and these do 
not exist in the lower ileum. The fluids swallowed are almost 
completely absorbed here, but their place is taken by the in- 
testinal secretions. The proteids are absorbed to the extent of 
85 per cent., more or less, before reaching the large intestine, 
and the carbohydrates almost entirely disappear. 

( C) From the Large Intestines. — The absorption process in 
the large intestine is quite active. The passage of the mass 
through it is slower, and even occupies an absolutely greater 
time than the journey through the much longer small intestine. 



128 ABSORPTION. 

The consistence of the contents progressively increases owing to 
continual absorption of the fluid portions, until the pultaceous 
mass received by the cecum becomes almost solid in the 
sigmoid. The degree of consistence may be said to be greater 
the longer the sojourn in the large intestine. The proteids and 
carbohydrates which have escaped absorption in the small in- 
testine are disposed of here, partly by bacterial decomposition, 
and do not appear as such in the feces. The absorption of easily 
digestible substances in solutions, such as eggs, etc., from the 
lower bowel, although there is no digestive enzyme there, is a 
matter of common observation, but one which lacks explanation. 

Forms in Which the Different Classes are Absorbed, i. 
Water and Salts. — Of course, water is absorbed in connection 
with all the foods as a vehicle for them, but water and salts as 
such have been shown to be absorbed sparingly in the stomach. 
They are soon conveyed to the small intestine, where their rapid 
disappearance ensues. However, they may be absorbed any- 
where in the alimentary canal. The loss of the water from the 
alimentary mass in the upper small intestine is compensated 
for by the secretions, so that the fluidity of the contents is not 
materially affected until the colon is reached. Here absorption 
of water is active, and the mass becomes more and more solid as 
the rectum is approached. 

2. Proteids. — It is agreed that the first object of proteid di- 
gestion is to render the nitrogenous foods more diffusible. It is 
also agreed that the end products of such digestion, so far as 
alimentary absorption is concerned, are proteoses and peptones ; 
and the natural conclusion, supported by experimental evidence, 
is that these represent the forms in which the proteids are ab- 
sorbed. True, leucin, tyrosin, etc., further end products of 
proteolysis, are formed, but these cannot be absorbed. The opin- 
ion that proteoses and peptones are the absorbable forms of pro- 
teids is correct, for by far the largest part of these foods are ab- 
sorbed in this shape. It is supposed also that syntonin at least 



ABSORPTION OF DIFFERENT FOODS. .129 

can itself be sparingly absorbed from the alimentary canal, while 
the phenomena of rectal absorption would point to the conclu- 
sion that proteid absorption in other shapes is possible. Prac- 
tically, however, proteoses and peptones may be regarded as the 
products of proteid digestion, and their production as the object 
of proteolysis. 

But, although these substances are absorbed by the blood-ves- 
sels, the artificial injection of them into the veins occasions un- 
toward effects, or at least their rejection through the organs of 
excretion. Furthermore, proteoses and peptones cannot be de- 
tected in the blood during alimentary absorption. It follows, 
then, that in their passage from the alimentary canal to the blood 
they undergo some change whereby they lose their identity and are 
no longer recognizable as such. It is claimed that they are con- 
verted into serum-albumin, and this is probably true. One ef- 
fect at least of the change is that they are now (in the blood) 
less diffusible, more complex, and consequently remain more 
easily a constituent part of that fluid. 

The proteids enter the radicles of the portal vein. 

3. Carbohydrates. — The sugar of the blood is dextrose, and 
if cane sugar be introduced into the veins it is rejected by the 
urine without being changed. It may be said that, with a few 
exceptions, all the carbohydrates are converted into dextrose or 
dextrose and levulose, before entering the blood. This form of 
sugar is easily oxidized in the tissues. It is conveyed directly 
to the liver by the portal vein. 

4. Fats. — The digestive end of the fats has been seen to 
be emulsions and soaps. They pass into the intestinal lymphatics, 
or lacteals. Their absorption is a mechanical process. They 
enter and pass through the epithelial cells and basement mem- 
brane of the villus. Having thus passed into the stroma of the 
villus, their entrance into the lacteal is easy \ for undoubtedly 
lymph spaces in the stroma are connected with the stomata of 
the central lymph capillary, and there is a more or less constant 



130 ABSORPTION. 

flow of lymph through these spaces toward the lacteal. The 
tendency, therefore, of the fats to enter the lacteal is physically 
natural. It is a curious fact that the peptones and sugars, having 
penetrated the lining epithelium of the villus, enter the blood 
instead of the lymph capillaries. 

A number of circumstances, such as the rate of absorption, 
the persistent direction of the current toward the blood in the 
face of superior pressure, the disappearance of non-osmotic sub- 
stances from the canal, etc., are frequently at variance with 
laboratory experiments. Application of the laws of osmosis to 
the vital processes is seemingly subject to many variations, and 
explanation of many of the phenomena of absorption in the 
body waits upon a clearer understanding of the so-called " vital 
activity " of the tissues. 

Resume of Absorption. — Absorption from the alimentary 
canal follows digestion and is dependent upon osmosis. The 
foods can be absorbed from that part of the canal in which they 
are digested, and speaking roughly, this may be said to occur ; 
but this statement is subject to modification as the result of on- 
ward movements of the food. (1) The inorganic foods are ab- 
sorbed throughout the whole gastro-intestinal tract, but mainly 
in the small intestine. (2) Proteid absorption begins in the 
stomach, is most marked in the small intestine and is concluded 
in the colon. (3) Carbohydrates are absorbed slightly in the 
mouth and stomach, but chiefly in the small intestine and slightly 
in the large intestine. (4) Fats are absorbed in the villous 
region of the small intestine. All foods, except fats, are ab- 
sorbed by blood-vessels, and go almost entirely to the liver 
through the portal vein. The fats are absorbed by the intesti- 
nal lymphatics, the lacteals, and go indirectly to the blood-cur- 
rent through the thoracic duct into the left subclavian vein. It 
is claimed that while the offices of the intestinal blood and lymph 
capillaries are thus clearly defined as regards the food they ab- 
sorb, they slightly overlap each other in their action, and are 
consequently not mutually exclusive as regards this function. 



CHAPTER V. 
THE CIRCULATION. 



All the cells in the body are continually producing effete 
materials and must consequently be continually appropriating 
new matter if they are to continue to live and functionate. This 
new matter is supplied to the cells by the blood, and it is only 
for this purpose — that of a vehicle — that the blood and circula- 
tion exist. The circulating fluid is not depleted in health be- 
cause its supply of nutritive materials is being continually re- 
plenished by the entrance of oxygen from the lungs and of the 
products of alimentary digestion. Nor does it become over- 
charged with effete materials, because they are being continually 
removed by the excretory organs. 

Since the cells not only need to appropriate the nutritive 
materials furnished by the ordinary foods, and to discharge the 
effete solids and liquids of metabolism, but also to appropriate 
and discharge gases — oxygen and carbon dioxide — two systems 
of circulation are provided, the systemic and the pulmonary. 
The systemic supplies with solid, liquid and gaseous nutriment 
all the tissues throughout the body ; it likewise collects, directly 
or indirectly through the lymph, from those tissues the solid, 
liquid and gaseous materials which are no longer useful and 
which are to be eliminated. On the other hand, the pulmonary 
circulation exists solely for the purpose of ridding the blood of 
carbon dioxide and of supplying it with oxygen. It will, there- 
fore, be necessary to consider (I) the mechanism of the circu- 
lation and (II ) the blood itself. 

131 



I 3 2 



CIRCULATION. 



(I) MECHANISM OF THE CIRCULATION. 

The study of the mechanism of circulation may be conven- 
iently divided into a consideration of the (A) heart, (B) arte- 
ries, ( C) capillaries and (Z>) veins, together with whatever may 

be known concerning phenomena 



Fig. 31. 




Scheme of the Circulation. 

a, right, b, left, auricle ; A, right, B, 
left, ventricle; 1, pulmonary artery; 
2, aorta; 1, area of pulmonary, K, 
area of systemic, circulation; o, the 
superior vena cava ; G, area supply- 
ing the inferior vena cava, u ; d, d, 
intestine ; m, mesentric artery ; q, 
portal vein ; L, liver ; h, hepatic vein. 
(Landois.) 



occurring in connection with the 
passage of blood through each. 

(A) The Heart. 

Anatomy. — The heart is bilateral, 
and may be considered as consisting 
of two separate but similar organs, 
each having two cavities, an upper 
and a lower, analogous in shape and 
function to the corresponding cavi- 
ties on the opposite side. As it is, 
these two organs, right and left, are 
applied and connected the one to 
the other, but there is no communi- 
cation between them except indi- 
rectly through the vessels which run 
to and from them. The right heart 
exists only for the purpose of keep- 
ing up the pulmonary circulation. 
Since the two sides of the heart act 
synchronously it will be unneces- 
sary, in describing the various move- 
ments, etc., to consider them sepa- 
rately. 

The human heart is a cone-shaped, 
hollow, muscular organ situated in 
the thoracic cavity behind the ster- 
num. Its base is in the median line 
and looks backward, upward and to 



THE HEART. 133 

the right ; its apex is three inches to the left of the median line 
in the 5th intercostal space and looks forward, downward and to 
the left. Its weight in the male is 10-12 ounces, in the female 
some 2 ounces less. It is held in place by the great vessels 
which run off from its base to be attached to the posterior wall 
of the thorax. The heart rests by about the apical half of its 
posterior surface upon the upper surface of the diaphragm. The 
main portion of the anterior (upper) surface consists of the right 
ventricle ; the main portion of the posterior (under) surface con- 
sists of the left ventricle. The left ventricle continues farther 
forward than the right and constitutes the apex of the heart. 

From the diaphragm is sent over the surface of the heart a 
double fold of the serous lining of the thoracic cavity, which is 
here known as the pericardium. The pericardial sac is of a 
cone shape with its base downward on the diaphragm and its 
apex upward embracing the origin of the great vessels, so that 
the relative positions of the apex and base of the heart and peri- 
cardial sac are the reverse of each other. Leaving the dia- 
phragm the pericardium runs upward over the heart, but not in 
contact with its substance, until it has passed a little way beyond 
the base and has enveloped the vessels * then it turns backward, 
folded inward upon itself, to cover closely, from base to apex, 
the whole extent of the viscus, and to leave an interval between 
it and the outer (upward) layer. The outer layer consists of an 
outer fibrous and an inner serous division ; it is only the serous 
layer which is reflected backward over the heart, the fibrous 
being continuous with the fibrous tissue in the vessel walls. Thus 
it is that the heart is covered by a slippery membrane which is 
enclosed by a second equally slippery. These membranes secrete 
a small amount of fluid for lubrication, and the friction of the 
beating heart is thereby reduced to a minimum. The amount of 
fluid in the pericardial sac is usually about one drachm. 

The cavities of the heart are lined by a thin serous membrane 
similar to the visceral pericardium called the endocardium. 



[ 34 



CIRCULATION. 



The heart has four distinct cavities, two on each side — one at 
the base, the auricle, and one at the apex, the ventricle ; the 
latter is the larger. 

The Right Auricle. — This cavity has a small sinus running 
off from it anteriorly known as the auricular appendix. There 



Fig. 32. 




Interior of Right Auricle and Ventricle Exposed by the Removal of a Part 
of their Walls. (From Yeo after Alle?i Thompson.) 

1, superior vena cava; 2, inferior vena cava; 1' , hepatic veins; 3, 3', 3", inner wall of 
right auricle ; 4, 4, cavity of right ventricle; 4', papillary muscle ; 5, 5', 5", flaps of tricuspid 
valve ; 6, pulmonary artery in the wall of which a window has been cut ; 7, on aorta near the 
ductus arteriosus; 8, 9, aorta and its branches; 10, 11, left auricle and ventricle. 



THE HEART. 



135 



are these openings into the right auricle : ( 1 ) Those for the two 
vence cavce, (2) the orifice of the coronary vein, (3) the foramina 
Thebes ii, and (4) the auric ulo -ventricular. The foramina The- 
besii are the orifices of small veins bringing blood from the 



Fig 




The Left Auricle and Ventricle Opened and Part of their Walls Removed 
to Show their Cavities. (From Yeo after Allen Thompson.) 

1, right pulmonary vein cut short; x' , cavity of left auricle; 3, 3", thick wall of left ven- 
tricle ; 4, portion of the same with papillary muscle attached ; 5, the other papillary muscles ; 
6, 6', the segments of the mitral valve, 7, in aorta is placed over the semi-lunar valves. ( Yeo. ) 



136 CIRCULATION. 

heart substance, though most of it enters by the coronary vein. 
The auriculo-ventricular opening is the communication between 
the right auricle and ventricle. 

The valves are the (1) coronary and (2) Eustachian. The 
coronary is a semicircular fold of the endocardium preventing 
regurgitation into the coronary vein. The Eustachian is a 
similar fold between the orifice of the inferior vena cava and 
the auriculo-ventricular opening. In fetal life it is supposed to 
direct the current of blood toward the foramen ovale. The 
fossa ova/is is a depression in the septum auriculorum represent- 
ing the fetal foramen ovale, and the annulus ova/is is the promi- 
nent margin of the same. 

The Right Ventricle. — This is below the right auricle. It 
is conical in shape. It extends nearly to the apex. 

The ope?ii7tgs in this cavity are (1) the auriculo-ventricular 
and (2) that for the pulmonary artery. The auriculo-ventricular 
is at the base of the ventricle, is about an inch in diameter and 
is guarded by the tricuspid valve. The opening for the pulmo- 
nary artery is near the septum ventriculorum. 

The valves are the ( 1 ) tricuspid and ( 2 ) pulmonary semilunar. 
The tricuspid valve guards the auriculo-ventricular opening and 
consists of three triangular segments attached by their bases to 
the circumference of the orifice. Each is a double fold of endo- 
cardium between the layers of which, extending nearly up to the 
free edge, is some fibrous tissue ; this arrangement makes the 
free approximating edges thin and pliable, while the remainder 
of the cusp is thicker and stouter. The division into three 
separate segments is frequently not distinct at their bases. 

Attached to the ventricular surfaces of these cusps are the 
chorda tendinecE, which are delicate but stout inelastic bands ; 
most of them are attached by their opposite ends to the 
papillary muscles. The columnce carnece are muscular columns, 
some of the mare simple ridges running along the inner sur- 
face of the ventricular wall ; some are rather thick muscular 



THE HEART. 1 37 

bands attached by their two extremities to the wall • while a 
third set constitute the ma $ cull papilla res, projections of mus- 
cular substance, more or less conical in shape, giving origin by 
their apices to most of the chordae tendineae. There are pri- 
marily only two of these muscles, but they subdivide into a large 
number. Some of the chordae tendineae spring directly from 
the muscular wall. 

The semilunar valves guard the opening of the pulmonary 
artery. They are three entirely separate segments of semi- 
lunar shape. They are attached by their long curved margins to 
the circumference of the artery just where it springs from the 
muscular substance of the ventricle. The three completely sur- 
round the orifice. They are of the same structure as the tri- 
cuspid. The free straight border of each cusp has running 
along it a very delicate band of fibrous tissue, while just in the 
center of this border is a small fibrous nodule, the corpus Arantii. 
From the corpus radiate toward the attached convex border of 
the leaflet delicate inelastic fibers. But on either side of the 
corpus Arantii is a small crescentic area in w'hich no fibrous 
tissue is interposed between the two layers of the serous mem- 
brane. These little crescents, lunula, reach by one of their tips 
the corpus Arantii, by the other the attached border of the seg- 
ment. When the valves project into the artery during the 
passage of blood through the opening they do not lie in contact 
with the arterial wall because there is a kind of pouch in the 
artery behind each segment, the sinus of Valsalva. 

The Left Auricle. — This, like the right, presents a main cavity 
and an auricular appendix. The openings are (i) those of the 
four pichno nary veins and (2) the auriculo-ventricular. The two 
veins from the left lung often unite before they reach the heart so 
that there are only three pulmonary openings. The auriculo- 
ventricular opening is a little smaller than the one on the right. 

The Left Ventricle. — This is the most interesting of the car- 
diac divisions. 



138 CIRCULATION. 

The openings are ( 1 ) the auriculo-ventricular and ( 2 ) the 
aortic. The auriculo-ventricular opening is below and to the 
left of the aortic orifice. 

The valves are the ( 1 ) 7?iitral and ( 2 ) aortic semilunar. The 
mitral valve guarding the auriculo-ventricular opening, resem- 
bles in general structure and function the tricuspid, except that 
it has two instead of three cusps and is thicker and stouter, as 
are the chordae tendineae attached to it. Smaller segments are 
frequently placed between the angles of the two flaps. The 
semilunar valves do not differ from the pulmonary semilunar, 
except that they are larger, thicker and stronger. The corpora 
Arantii are also larger. The sinuses of Valsalva are present in 
the aorta as in the pulmonary artery. The columnce carnece 
are more numerous and intricate than in the right ventricle. 
There are here also two primitive musculi papillares. The sep- 
tum ventriculorum is thicker than the septum auricularum, ex- 
cept toward the base of the ventricles where it is thin and 
fibrous. 

The average thickness of the walls of the several cavities is- as 
follows : right auricle one-twelfth inch, left auricle one -eighth 
inch, right ventricle one-sixth inch, left ventricle one -half inch. 
These differences are in accord with the muscular work required 
of each division. 

Capacities of the Cavities. — The auricles are about one-third 
less capacious than the ventricles. 

The absolute capacity of any of these cavities under normal 
conditions is a subject of speculation, but probably the ventri- 
cles ordinarily expel at each systole about four ounces of blood 
each. They must expel equal amounts, and their capacities are 
at least practically the same. 

Structure. — In structure the heart consists of fibrous rings 
surrounding the orifices and of muscular fibers attached to these. 
The muscular fibers of the auricles and ventricles are inde- 
pendent of each other. The auricles have (1) a superficial set 



COURSE OF BLOOD. 1 39 

of fibers common to both, and (2) a deep layer proper to 
each. The superficial set run as a rule transversely ; some of the 
deep set loop from the fibrous margin of the auriculo-ven- 
tricular opening over each auricle, while others run circularly. 
The ventricular fibers may be said in a very general way to be 
disposed in the same manner as the auricular. They compose a 
very intricate and complete network, the contraction of which 
practically obliterates the ventricular cavities. It seems that at 
least some of the longitudinal fibers dip into the substance of 
the heart at the apex to form the columnse carneae. 

The blood supply of the heart is furnished by the coronary 
arteries. 

Course of Blood Through the Heart and Vessels. — The right 
auricle receives all the venous blood from every part of the 
body — from the head and upper extremities through the vena 
cava descendens, from the trunk and lower extremities through 
the vena cava ascendens, and from the heart muscle through the 
coronary sinus and the foramina Thebesii. 

From the right auricle the venous blood enters the right ven- 
tricle through the right auriculo-ventricular opening \ thence it 
is passed to the lungs through the pulmonary artery. Having 
traversed the pulmonary capillaries and become arterialized, it 
converges to the two pulmonary veins in each lung ; these con- 
vey it to the left auricle which passes it through the left auriculo- 
ventricular opening into the left ventricle ; being forced out of 
this cavity through the aortic opening into the aorta, it is dis- 
tributed to all parts of the system, traverses capillaries, becomes 
venous and is collected to be carried back to the right auricle and 
begin the circuit again. 

Ordinarily blood passes through only one set of capillaries 
before being returned to the heart, but the blood of the portal 
vein, having already passed through the capillaries in the ali- 
mentary canal, spleen and pancreas, must traverse the hepatic 
system of capillaries as well. The blood of the renal vein also 



140 CIRCULATION. 

passes through two systems of capillaries in the kidney 
substance. With the exception of the pulmonary artery (and 
its branches) which carries venous blood, and the pulmo- 
nary veins which carry arterial blood, arteries normally contain 
arterial and veins venous blood. The departure from the rule 
in the nomenclature of these vessels is warranted by their struc- 
ture, functions, etc. 

Contractions of the Heart. — The ventricles operate as a pair 
of pumps, the action of which is somewhat modified by the 
presence of the auricles. Their contractions force the blood on 
the one hand into the lungs and on the other into the systemic 
circulation, while in the interval of their contractions they are 
filled partly by the action of the auricles. Both auricles and 
both ventricles contract at exactly the same time and in the 
same manner, so that a description of the mechanism of one 
side is sufficient to explain that of both. 

Each cavity of the heart undergoes periodic contractions when 
it forces out the contained blood, and periodic dilatations when 
it is receiving blood. The contraction is the systole and the 
dilatation the diastole. These terms have come to refer to the 
contractions and dilatations of the ventricles only, unless the 
adjective "auricular" be prefixed. 

When the heart of a living animal is exposed by opening the 
chest and pericardial sac it can be seen that there is a regular 
succession of cardiac movements followed by periods of rest. 
Beginning with the auricle, it is found that it receives blood 
from the incoming veins during most of the cardiac cycle — dur- 
ing all of it except the short period occupied by its systole. 
The auricular dastole is, therefore, much longer than the auric- 
ular systole. When the cavity has been filled the auricle con- 
tracts suddenly and forces its contents into the ventricle. Re- 
gurgitation into the veins may occur to a slight degree, but the 
contraction of the auricular fibers surrounding the venous open- 
ings together with the relatively large auriculo-ventricular orifice 
insures the passage of the blood into the ventricle. 



CHANGES IN HEART. 141 

Previous to, as well as during, the auricular, and subsequent 
to the ventricular, systole, blood is entering the ventricle from 
the auricle. When the auricle contracts the addition of its 
blood to that which has already entered the ventricle completely 
fills it and brings on ventricular systole. The blood, prevented 
from regurgitating into the now dilating auricle by the auriculo- 
ventricular valve, forces the semilunar valve and enters the 
pulmonary artery (or the aorta as the case may be). As soon 
as the ventricle has emptied itself it begins to dilate slowly 
and continues to do so until another auricular systole com- 
pletely fills it. The ventricular diastole is also longer than its 
systole in health. 

The heart is in complete repose in all its parts from the end 
of ventricular to the beginning of auricular systole. During 
that time both cavities are in diastole, but it does not embrace 
the entire diastolic period of either. 

Changes in Shape and Size of the Heart and Arteries. — In 
diastole the muscular walls of the heart are soft and flaccid ; in 
systole they are hard and firm. During systole the cavities de- 
crease in size ; during diastole they progressively increase to the 
maximum at the beginning of the succeeding systole. There is 
no change at any time in the actual size of the heart muscle, but 
in that of the cavities. Ventricular systole charges the greatr 
arteries, already full, with an additional amount of blood, causing 
them to expand and lengthen ; during diastole they shorten and 
shrink. 

The changes in size, position, etc., of the beating heart are 
connected almost entirely with the action of the ventricles. 
Their contraction makes the heart harder, smaller in circum- 
ference and shorter, but more pointed. The apex is also raised 
slightly and sweeps toward the right, while the whole organ is 
twisted upon itself in the same direction, and is protruded 
against the chest wall, notwithstanding the shortening of its long 
diameter. 



I42 CIRCULATION. 

The fact that the heart becomes harder, smaller and shorter 
in systole, considering that it is a hollow muscular organ, cor- 
responds with muscular contractions elsewhere. The twisting 
of the heart, the raising of the apex and its movement toward 
the right are mechanical consequences of the course of the ven- 
tricular fibers. The fact that the organ is shortened in systole, 
together with the protrusion of the apex against the chest wall, 
presupposes the locomotion of the organ forward away from the 
posterior chest wall. This is what occurs, and it is caused by 
the sudden distention and lengthening of the great arteries at 
the base. When the auricles are properly exposed they can be 
seen gradually to enlarge the base of the heart during their 
diastole, but they do not push it forward for obvious reasons. 
Their walls are so thin that their color is affected by the contained 
blood, the right having a dark blue and the left a red color. 

The apex beat, or impulse, of the heart can usually be seen 
or felt in the fifth left intercostal space. This beat takes place 
upon ventricular systole, and is caused by the locomotion forward 
of the heart, the hardening of the ventricles and the movement 
of the apex upward and to the right. The beat, when the chest 
wall is thin, can be seen to move slightly upward and to the 
right during its production ; it is also noticed that immediately 
around the protrusion the tissues are slightly drawn in, owing 
doubtless to the "suction " of the contracting ventricles. 

Action of the Valves. — A thorough understanding of the ar- 
rangement and action of the cardiac valves is of the greatest im- 
portance. It is through their intervention that the heart is en- 
abled to keep the blood in circulation — and always in the same 
direction. Without them the pump would be useless, so much 
so that the smallest lesion of a single one of them may be fol- 
lowed by embarrassed circulation and subsequent death. 

The mitral and tricuspid valves are similar in their action and 
function and a description of the mechanism of the former can 
be applied to the latter. 



AURICULO-VENTRICULAR VALVES. 143 

Supposing that ventricular diastole has just begun, the two 
flaps hang loosely in the cavity of the ventricle, but probably 
not in contact with the wall. The blood, now continuously en- 
tering from the auricle, accumulates behind the flaps and floats 
them away from the walls, bringing their free edges toward each 
other, so that they are not very far apart at the beginning of 
auricular systole. When that systole occurs the sudden acqui- 
sition of the auricular contents so increases the intra-ventricular 
pressure as to bring together at once the free margins of the two 
flaps. 

These flaps are probably not approximated edge to edge, for 
thus it would seem impossible to prevent some regurgitation, 
but the auricular surfaces of the thin flexible portions of the free 
edges are apposed to each other, so that increased ventricular 
pressure would tend only to make the approximation firmer and 
regurgitation more impossible — within a certain limit. Since 
the forces thus holding together the apposed surfaces are equal 
and act one against the other, there is no strain upon these deli- 
cate portions of the cusps and they can, therefore, be left pliant 
enough to insure accurate adjustment. 

Those parts of the curtain, however, which intervene between 
the now approximated thin surface and the attachment at the 
auriculo-ventricular ring are subjected to considerable force and 
are consequently provided with fibrous tissue between the two 
serous layers. But without additional provision the flaps would 
still doubtless be forced back into the auricle during ventricular 
systole. This provision is in the shape of the chorda tendinece 
already described. They are small but strong and inelastic, and 
being attached to the ventricular surfaces of the flaps from the 
free margins to the bases, they serve as very efficient guy-ropes 
to prevent reversal into the auricle. Not only do the cords pull 
directly away from the auricle, but, as the size of the ring de- 
creases with the progress of ventricular systole, the cords at- 
tached to the lateral halves of a flap pull them in opposite di- 



144 



CIRCULATION. 



rections so as to keep the curtain taut. The papillary muscles, 
from which most of the chordae tendineae spring, probably pre- 
vent, by their contraction, the slacking of the cords as the cavity 
of the ventricle becomes smaller in systole. 

The semilunar valves have a simpler mechanism than the 
auriculo-ventricular. Each is composed of three cusps attached 
by their convex bases to the circumference of the arterial orifice 




Portion of the Wall of Ventricle. 

d, d' , and aorta, a, b, c, showing attachments of one flap of mitral and the aortic valves; 
h and g, papillary muscles; e, e' andy, attachment of the tendinous cords. (From Yeo 
after Allen Thompson.) 



SEMILUNAR VALVES. 1 45 

(Fig. 34) 1 the free edge is comparatively straight when the 
cusp is removed from its attachments. 

These valves have no chordae tendineae ; they are entirely de- 
pendent upon their attachment to the vessel wall to prevent re- 
versal. When the aorta is opened the flaps are found to form 
three pockets between their arterial surfaces and the adjacent 
wall of the vessel. They are convex toward the heart. Their 
object is to prevent regurgitation into the ventricle, and to do 
so they must not themselves be reversed into that cavity. They 
receive some support by being attached just where the thick 
muscular substance of the ventricle merges into the much thin- 
ner arterial wall. 

Suppose that blood is now entering the aorta; the flaps 
project into that vessel, but are not in contact with its walls. 
Blood is always in the sinus of Valsalva behind each cusp, and, 
as the entering volume during ventricular systole is continuously 
increasing arterial pressure, the curtains probably approach each 
other by their free edges before the end of that systole ; at the 
instant of its cessation the arterial pressure becomes much greater 
than the ventricular and the blood in the sinuses immediately 
forces together the free edges of the curtains which effectually pre- 
vent a backward flow of the current. The approximation of the 
flaps is further aided by the lessening of the aortic orifice as a re- 
sult of contraction of the ventricle. 

Here, as in the case of the auriculo-ventricular valves, the 
flaps are not joined edge to edge but by apposition of the ven- 
tricular surfaces of the narrow flexible lunula. These surfaces 
are pressed together by equal and opposite forces and do not, 
therefore, undergo any strain. Their flexibility provides for ac- 
curate adjustment except at the middle where the three cusps 
meet. Here is a triangular space which is just filled by the 
three corpora Arantii. 

The action of the pulmonary semilunar is the same as that of 
the aortic. 



146 CIRCULATION. 

Relative Condition of the Valves. — The auriculo-ventricular 
valve is open except during the ventricular systole ; the semi- 
lunar is closed except during the same systole. Thus the auric- 
ulo-ventricular is open during the greater part of the cardiac 
cycle, and the semilunar during the remaining smaller part. 
When one is opened the other is invariably closed. The auric- 
ulo-ventricular closes to prevent regurgitation into the auricle 
during ventricular systole and opens as soon as the systole is fin- 
ished ; the semilunar closes to prevent regurgitation into the ven- 
tricle from the recoil in the artery following systole, and is not 
opened until forced by the succeeding ventricular systole. 

When either valve is open blood is passing through the orifice 
which it guards. In the first part of the period during which 
the auriculo-ventricular is open blood is passing through slowly 
but freely, while during the latter part of that period, which 
is occupied by the auricular systole, it rushes forcibly through ; 
it passes with great force through the aortic and pulmonic 
openings during the whole time that the semilunar valves are 
open. 

The Cardiac Cycle. — A fair idea of the succession of events 
taking place in connection with the movements of the heart 
has been gathered from preceding remarks. The term "car- 
diac cycle ' ' is employed to embrace this whole succession of 
events occurring between the beginning (or ending) of any 
single event and the beginning (or ending) of that same event 
again. The point of departure may be taken anywhere, say, at 
the beginning of the ventricular systole ; in this case the cycle 
ends with the beginning of the succeeding ventricular systole 
and includes everything that has taken place meantime. 

The term " auricular cycle " or " ventricular cycle " may be 
similarly applied to the activity and succeeding repose of either 
of the cavities indicated. If we suppose the auricular cycle to 
begin with the contraction of the auricle that cycle will end and 
a second begin when the auricle begins to contract a second 



CARDIAC CYCLE. 147 

time. Thus the auricular cycle (or the ventricular) is equal in 
length of time to the cardiac cycle, but the terms are not syn- 
onymous because the latter refers to the succession of events in the 

whole heart. 

Fig. 35. 




Scheme of Cardiac Cycle. 
The inner circle shows the events which occur within the heart ; the outer the relation of 
the sounds and pauses to these events. {Kirkes after Sharfiey and Gairdner.) 

Occurrences During the Cycle.— As soon as the auricle is 
filled with blood from the supplying veins its systole occurs. 
The systole of the ventricle follows immediately. Then there 
occurs a "period of repose " for the whole heart— which repose 
is broken by the next systole of the auricle, and the same train 
of events recurs. 

The "period of repose " just mentioned does not cover all 
the rest which any one part of the heart gets 5 both auricle 
and ventricle rest a little longer than this. For the auricular 
diastole (rest) begins as soon as the auricular systole ceases, and 
this is previous to the beginning of the "period of repose " — 
by a time equal in length to the ventricular systole— and lasts 
until the end of the " period of repose " ; the ventricular dias- 



148 CIRCULATION. 

tole begins with the "period of repose" and lasts until the 
auricular systole has ceased, and this is subsequent to the end of 
the " period of repose " — by a time equal in length to that of 
the auricular systole. (See Fig. 35.) 

Thus the auricular diastole embraces the ventricular systole 
and the first part of the ventricular diastole ; the ventricular 
diastole embraces the latter part of the auricular diastole and the 
whole of the auricular systole. The auricular systole embraces 
the latter part of the ventricular diastole ; the ventricular sys- 
tole embraces the first part of the auricular diastole. The two 
cavities are never in systole together but are in diastole together 
during the "period of repose" (Fig. 35). 

During auricular systole blood is rushing into the ventricle 
through the auriculo-ventricular opening; during ventricular 
systole blood is rushing through the aortic (and pulmonary) 
orifice, and is also entering the auricle (whose diastole has be- 
gun) through the great veins. During the "period of repose " 
blood is entering the auricle through the great veins and is also 
passing freely through the auriculo-ventricular opening into the 
ventricle. As soon as the auricle becomes full it contracts and 
passes its contents to the ventricle ; this extra amount is suffi- 
cient to distend the ventricle and its contraction supervenes at 
once. 

Length of Cycle. — Since the heart beats about 72 times per 
minute each cardiac cycle must occupy .83 of a second, at this 
rate. When the rate is doubled the cycle is of course reduced 
one half. If the rate be 60 each cycle will have a length of 
one second. 

It is important that when the rate is increased, it is at the 
expense chiefly of the diastole, the systole requiring a length of 
time which varies little. Thus if the rate be doubled the heart 
will not get half so much rest as under normal conditions. 

If the cardiac cycle be divided into tenths it is reckoned that 
the auricular systole occupies a little less than .2, the ventricu- 



CARDIAC SOUNDS. 1 49 

lar systole a little less than .4, and the period of repose about 
.5. Reduced to their absolute values the estimates, when each 
cycle occupies .8 sec, are generally reported as .1 sec. for 
auricular systole, .3 sec. for ventricular systole, and .4 for the 
period of repose. These periods are, of course, only approxi- 
mate. 

Sounds of the Heart. — When the ear is applied to the chest 
in the precordial region two sounds may be heard which are 
evidently connected with the action of the heart. The first is 
heard at the time of the apex beat ; the second follows with 
scarcely an appreciable interval. After the second sound there 
is a pause before the recurrence of the first sound. The first 
sound is longer, lower in pitch than the second and somewhat 
muffled ; the second is comparatively short, high in pitch and 
clear. Both can usually be heard over the whole precordium, 
but the first is heard best toward the apex and the second toward 
the base. 

Since the first is heard at the time of the apex beat it corre- 
sponds in time with the ventricular systole and, from its dura- 
tion, must embrace practically the whole of that event. Since 
the second sound follows so quickly it must occupy the begin- 
ning of the ventricular diastole, but from its short duration must 
embrace only a small part of that event. (See Fig. 35.) 

What is the cause of the sounds ? The time of the first sug- 
gests that it is due directly or indirectly to the ventricular con- 
traction. The auriculo-ventricular valves close forcibly at the 
beginning of this event, and suggestion also points to them as 
being a factor in the production of the sound produced at that 
time. It is found, indeed, that the first is a compound sound in 
that it is produced in part by the valves and in part by other cir- 
cumstances ; it possesses a valvular and a non-valvular element. 
It has been shown by experiments that the sudden closure of 
the aitriculo -ventricular valves is attended by a sound — and this 
is the main factor in the production of the first cardiac sound. 



150 CIRCULATION. 

To it are to be added the muscular sound attending the contrac- 
tion of the heart, the impulse of the apex against the chest wall 
and possibly the vibrations of the chordae tendineae. It is the 
muscular contraction and the apical impulse which give to the 
first sound its prolonged, muffled, booming character ; were 
there only a valvular element this sound would probably be very 
similar to the second in character and duration. 

The second sound is simpler in its production. It is purely 
valvular and is caused by the sudden closure of the aortic and 
pulmonic semilunar valves. 

Succession of Events in Relation to the Sounds. — It is of prime 
importance, especially in pathological lesions of the valves, to 
know exactly what is occurring in all parts of the heart during 
the production of each sound and during the pause (Fig. 35). 
Knowing what causes these sounds and the sequence of events 
in the cardiac cycle this is easy. 

Since the first sowid is produced partly by, and is continued 
throughout, the ventricular systole it follows that during its pro- 
duction the auricle is in beginning diastole and is receiving 
blood from the veins \ the auriculo-ventricular opening is closed ; 
blood is rushing through the aortic (and pulmonic) orifice, and 
the semilunar valves are open. 

Since the second sound is caused by closure of the semilunar 
valves and just follows the ventricular systole, during its pro- 
duction the auricles are still swelling and receiving blood from 
the veins ; the auriculo-ventricular valves are opening and blood 
is beginning to enter the ventricles ; the ventricular diastole is 
beginning ; the semilunar valves are closed. 

The pause, following the second sound, lasts until the begin- 
ning of the following ventricular systole. During the first part 
of that time the auricle is receiving blood from the veins and 
completes its diastole ; during the latter part the auricular systole 
occurs 1 during the whole pause the auriculo-ventricular valve is 
open and blood is passing into the ventricle, at first slowly, then 



WORK OF THE HEART. 151 

forcibly ; the ventricle completes its diastole \ the semilunar 
valves are closed. 

It is to be noticed that the auricular systole is accompanied by 
no sound appreciable to the auscultating ear. 

If the foregoing circumstances be once clearly grasped there 
will be little difficulty in determining the location and character 
of at least the more common valvular lesions in disease. 

Attention is called to the fact that the "period of repose" 
and the "pause" are not identical in time. They are of about 
equal length, but it is seen that the pause begins and ends a 
little later than the period of repose. The former covers the 
period when no sound can be heard \ the latter when no muscu- 
lar contraction is in progress. In Fig. 35 the space marked 
" Diastole of Auricle and Ventricle " does not embrace the en- 
tire diastole of either. 

The first sound occupies a little less than .4 of the cardiac 
cycle ; the second sound some .2, and the pause the remainder. 

Work of the Heart. — In estimates of the work accomplished 
by the cardiac contractions there are the widest variations 
among different observers. The figures of some are even twice 
those of others. The chief difficulty is in determining the 
amount of blood ejected at each ventricular systole. No ac- 
curate idea of this amount — the " pulse volume" — can be ob- 
tained from the size of the cavity when filled post mortem ; the 
varying conditions of pressure, etc., cannot be imitated properly. 
Nor is it probable that the ventricles completely empty them- 
selves during systole, a small, but variable, amount of blood re- 
maining in unobliterated spaces just below the valves. The 
figures below given in connection with the subject are from the 
American Text-book of Physiology. It is not claimed there 
that they are accurate. 

The amount of blood thrown into the arteries by the two ven- 
tricles at each contraction must be equal or there would be an 
accumulation in either the pulmonary or systemic circulation. 



152 CIRCULATION. 

When the circulation is evenly carried on the amount of blood 
entering the capillaries of either system during a cardiac cycle 
must be equal to the amount thrown into the artery — the pulse 
volume — at one ventricular systole. While it is apparent that 
the pulse volume is subject to variations from almost numberless 
causes the average will be taken as 100 grams (about 3 oz.). 

To find the amount of work done by each ventricular systole 
it is necessary to multiply the pulse volume by the pressure 
which ejects it. It is found that the maximum pressure in the 
left ventricle will raise mercury in a small tube inserted into the 
cavity 200 mm., and in the right ventricle 77 mm. If blood be 
substituted for mercury it will rise from the left ventricle 2.567 
m., and from the right .988 m. That is, the contraction of 
the left ventricle would raise the pulse volume 2.567 m. and 
that of the right .988 m. The two together would raise the 
pulse-volume (100 gm.) 3.555 m. Then the work done by 
both ventricles will be equal to 100 gm. x 3-555 m., which 
gives a product of 355.5 grammeters for each double ventricular 
systole. A gra??imeter is a unit of work corresponding to the 
foot-pound, and represents the amount of force required to raise 
one gram one meter. 

355.5 grammeters are equal to about two foot-pounds, which 
may be taken as representing the amount of work done by each 
contraction of the ventricles ; that is, every time the ventricles 
contract they do enough work to raise one pound two feet, or two 
pounds one foot. Considering the rate of the cardiac contractions 
it is evident that an enormous amount of work is done in a day 
by this one muscle. These figures are rather below those of 
most authors. The work done by the auricles is so small as 
to be disregarded. 

The force exerted by the left ventricle at each contraction 
has been estimated at 52 pounds. This result is obtained by 
multiplying the weight of the pulse volume by the supposed area 
of the internal surface of the ventricle. 



INNERVATION OF THE HEART. 1. 5 3 

Ventricular Pressure. — This subject has been touched upon 
in the foregoing section, but besides the maximum pressure 
there mentioned there is also a minimum pressure in this cavity. 
The maximum pressure was given as 200 mm. of mercury; the 
minimum is found to be — 40 mm. Now, the pressure in the 
aorta (or any artery) varies within certain limits, but is always 
positive ; that in the ventricle while at its maximum exceeds 
that in the aorta and so opens the semilunar valve, but while at 
its minimum it not only falls far below that of the artery, allow- 
ing the closure of the valve, but becomes actually negative — 
below the atmospheric pressure — and exerts a " suction ' ' force. 

At this time it is below the auricular pressure and thus the 
auriculo-ventricular valve is opened. This negative pressure in 
the ventricle is due to two causes : ( 1 ) Aspiration of the thorax, 
and (2) tonicity of the heart muscle itself. The latter element 
is not very active ; the former is much more efficient during 
inspiration, and may cease to operate during expiration. 

Functions of the Auricles. — The maximum systolic pressure 
in the auricle is only some 20 mm. of mercury ; the minimum 
diastolic pressure is about — 10 mm. The small positive pressure 
is adequate for the work to be done ; for the auricle has no valve 
to force in systole and the ventricular pressure at that time is 
very little if at all above the atmospheric pressure. Its contrac- 
tion serves to fill the ventricle and bring on ventricular systole, 
but its action is not indispensable in circulation. It serves as a 
reservoir, providing for a much more even flow of blood from the 
veins than would be the case if the vessels entered the ventricle. 

Whether the auricle completely empties itself by systole 
and whether blood continues to enter from the veins during its 
systole are matters of dispute. 

Innervation of Heart. — The rhythmical contraction of the 
heart are kept up by (1) the cardiac branches of the vagus, (2) 
the cardiac branches of the sympathetic, (3) the intrinsic ganglia 
of the heart. 



154 CIRCULATION. 

Accurate knowledge of the course, distribution and action of 
these fibers is wanting because there are so many points of dif- 
ference in the lower animals. The following facts seem to be 
true in case of the rabbit : 

Running upward from the inferior, middle and superior cervical 
sympathetic ganglia are three nerves — inferior, middle and su- 
perior cardiac. These, joining a branch from the pneumogas- 
tric at a point near its exit from the cranium, form with it the 
vago-sympathetic trunk, the fibers of which pass to the heart and 
enter superficial and deep plexuses in which are gangli- 
onic aggregations ; they pass thence to the heart, entering with 
the inferior vena cava. They thus reach the ganglion of Remak 
in the expansion of that vessel (sinus venosus), and run from 
this point to the ganglion of Ludwig between the two auricles 
and to the ganglion of Bidder in the left auriculo-ventricular 
septum. 

From these ganglia radiate three plexuses to the pericardium, 
myocardium and endocardium. The ganglia of Remak and 
Bidder are motor in function ; that of Ludwig is inhibitory. 

Stimulation of the sympathetic fibers before they join the 
vagus increases the frequency and diminishes the force of the 
heart. Stimulation of the vago-sympathetic trunk produces aug- 
mentation — increased force and frequency. Stimulation of the 
vagus before junction produces inhibition of the heart's action, 
increasing the force but diminishing the frequency (direct 
action). 

Just after leaving the cranial cavity the vagus receives certain 
fibers from the spinal accessory which run with it and are 
distributed to the heart. It is through these fibers that the 
direct inhibitory action of the ioth nerve occurs. 

Furthermore, there has been found a nerve rising by two roots — 
one from the trunk of the pneumogastric and the other from the 
superior laryngeal — which joins the sympathetic filaments in the 
chest and passes to the heart. The root from the superior laryn- 



CARDIAC RATE. I 5.5 

geal probably comes from the spinal portion of the spinal accessory 
through the ganglion of the trunk of the vagus. This nerve is 
known as the " depressor vagi," or the depressor nerve of the 
circulation. It is a centripetal nerve. If it be cut stimulation 
of the peripheral end produces no effect on the heart, but stimula- 
tion of the central end inhibits cardiac action and lowers arterial 
tension. Its action is, therefore, reflex only. But this nerve 
must act in conjunction with the sympathetic, for it inhibits 
cardiac action only by stimulating the vaso -motor center to dilate 
the peripheral vessels. Its normal function is to adapt the 
heart's action to the peripheral resistance. If the splanchnic 
be cut the fall in blood-pressure is very slight, showing that 
the splanchnic area is the one most affected. 

In the human being the depressor nerve fibers are probably 
bound up in the vagus trunk. 

Therefore, heart action is accelerated by stimulation of the 
sympathetic supply ; it is augmented by stimulation of the vago- 
sympathetic trunk ; it is inhibited directly by stimulation of the 
vagus before it is joined by the sympathetic, and reflexly by 
stimulation of the depressor vagi. 

Frequency of Heart Beat. — In the normal adult the heart 
rate is usually given as 72 per min. for the male and 80 for the 
female. 

A very great many not abnormal circumstances cause the rate 
to vary. It is more rapid in tall than in short persons, and this 
partially explains the different rate for the sexes ; but women of 
the same height as men have a faster pulse than those men. The 
fetus has a cardiac rate of from 1 20 to 150, and even here the differ- 
ence in the sexes is evident ; so much so that the rate has been 
made use of as giving some indication as to the sex. During the 
first year it declines to about 120 and after that time gradually 
diminishes to adult life. At puberty the difference for the sexes 
becomes more marked. There is a slight acceleration in old 
age. The digestion of an ordinary meal increases the frequency 



156 CIRCULATION. 

some 5-10 beats ; fasting diminishes it ; nitrogenous foods in- 
crease it more than non-nitrogenous. Muscular exercise increases 
it markedly and in proportion to the violence of that exercise. 
Posture influences it ; for the male the average rate standing is 
80, sitting 72, lying 65 ; this variation is not due entirely to 
the muscular exercise necessary in standing or sitting. The rate 
is diminished during sleep ; this is a probable effect of the 
total freedom from muscular strain or exercise and the absence 
of any emotional factors. High external tempe7'ature increases 
it ; cold diminishes it. Emotional distiwbances are very effective 
in usually increasing the frequency. Respiration has a marked 
influence. Commonly the respiratory and cardiac rates increase 
and decrease together. During inspiration the cardiac rate is a 
little more rapid ; during expiration it is a little slower. But 
arrest of respiration in any phase very soon slows the heart and 
finally, if not relieved, stops it for two reasons. First, any 
muscle deprived of fresh blood soon loses its power to contract, 
and the heart is no exception. Second, when blood is not 
oxygenated it will pass through the capillaries only with the 
greatest difficulty. As a consequence it accumulates in the 
arterial system, dams back upon the heart and so distends that 
organ as to paralyze it. 

• Arrest of the Heart. — Asphyxia, from any reason, if prolonged, 
will cause the heart to stop as just described. It is the second 
(mechanical) reason which is chiefly operative in death from 
asphyxia, although the first would be equally effective in time. 
Engorgement, whether with or without asphyxia, often causes 
arrest of the heart's action.. When the heart is deprived of its 
own blood supply, as by embolism of the coronary artery, it 
very soon ceases to act. It is also arrested by removal of its 
ordinary stimulus, the blood, passing through its cavities. This 
is the chief cause of death from hemorrhage ; hence the value 
of injections of salt solutions into the circulation. Blows in the 
epigastric region may cause death by arrest of the heart. It is 



THE ARTERIES. I 57 

not known whether this is an effect of direct violence to the 
organ or to the solar plexus through which the nervous equilib- 
rium is disturbed. Arrest of the heart by nervous influences 
seems, as already indicated, to take place through the pneumo- 
gastric. The heart may, therefore, be said to be stopped by 
any one of three causes : ( i ) distention, ( 2 ) loss of blood, ( 3 ) 
nervous disturbances. 

(B) The Arterial Circulation. 

Objects of Arterial Circulation. — The arteries exist primarily 
for the purpose of conveying to the capillaries the blood 
received from the ventricles — the object of the conveyance to 
the capillaries being, in the pulmonary circulation, the inter- 
change there of gases between the blood and air, and in the 
systemic circulation, the interchange of gases and nutritious 
and excrementitious materials between the blood and cells of 
the tissues. No such interchanges take place in the arteries ; 
the blood must reach the capillaries before they can occur, and 
the arteries furnish the routes by which it does so. 

But these vessels are so constituted as not to be simple passive 
tubes through which the current runs \ they have, by virtue of 
their structure, two very important additional offices : first, they 
change the forcible intermittent flow received from the ventricles 
into a steady constant one by the time the capillaries are reached • 
second, they regulate the amount of blood going to a part 
at different times, thus properly distributing the fluid over the 
body in obedience to the varying demands of particular organs. 
"The movement of the blood depends on the heart, but its 
distribution depends on the vessels. ' ' 

Anatomy. — The vessel carrying all the blood away from the 
right ventricle to the pulmonary circulation is the pulmonary 
artery ; the blood to the systemic circulation leaves the left 
ventricle by the aorta. These divide, branch and subdivide, the 
divisions becoming smaller and smaller until the microscopic 



158 CIRCULATION. 

capillaries are reached. The combined caliber of the branches 
progressively increases as the number becomes larger. With few 
exceptions the combined capacity of any two bifurcating branches 
is larger than that of the dividing vessel. Consequently the 
capacity of all the small arteries in either system is far greater 
than that of the vessel leaving the ventricle. 

The pulmonary artery carries venous blood, but by structure 
and office it belongs to the arterial system. It is somewhat 
thinner and more distensible than the aorta, but otherwise its 
anatomy is similar. 

While all the arteries are to a certain extent identical in 
structure, they present differences which warrant their division 
into three classes : ( 1 ) large arteries, including the common 
carotids and common iliacs and those larger; (2) medium arte- 
ries, including all between (1) and (3) ; (3) smallest arteries, 
including all of a diameter of ^ inch and less. They all have 

three coats. 

Fig. 36. 




Transverse Section of Part of the Wall of the Posterior Tibial Artery 
(Man). (From Yeo after Shafer.) 
a, endothelium lining the vessel, appearing thicker than natural from the contraction of the 
outer coats ; b, the elastic layer of the intima ; c, middle coat composed of muscle fibers and 
elastic tissue; d, outer coat consisting chiefly of white fibrous tissue. 

Histology. — In the largest arteries the external coat, or 
tunica adventitia, is of fibrous tissue with a little plain muscular 
tissue ; it is no thicker than in the medium arteries. The 
middle coat, or tunica media, constitutes the main part of the 
wall. It consists chiefly of yellow elastic tissue, between the 



THE ARTERIES. I 59 

layers of which are a few plain muscle fibers. The internal 
coat, or tunica intima, consists of a single layer of endothelial 
cells upon a thin elastic supporting membrane. The cells are 
oval in shape, their long diameters being in the direction of the 
vessel. 

In the medium arteries, the external coat is practically iden- 
tical with that of the largest arteries. The middle coat, instead 
of presenting so much yellow elastic tissue, is made up mainly 
of plain muscle fibers. In the largest of this class the elastic 
tissue is abundant, being continued from the larger vessels, but 
it gradually gives place to muscular tissue as the branches be- 
come smaller, until before the smallest arteries are reached there 
is scarcely any elastic tissue left. The internal coat is the same 
as in the largest arteries. 

In the smallest arteries the external coat is the same as in 
the largest, except that it is thinner and disappears just before 
the capillaries are reached. The middle coat is of muscle fibers 
with no elastic tissue. The internal coat is the same as in the 
larger vessels. 

Of course, this division of the arteries is arbitrary, and they 
present no marked differences at the dividing lines mentioned. 
It is apparent that it is the middle coat which constitutes the 
chief difference, the elastic tissue of the large vessels giving 
place to muscular in the medium and smaller. It follows that 
the large arteries must be possessed of great elasticity and the 
medium and smaller of great contractility. These are, indeed, 
distinguishing characteristics, and of the very greatest impor- 
tance in the economy of the circulatory forces. 

Vessels called vasa vasorum penetrate the external, and to a 
less extent the middle coats, supplying them with nutriment ; 
they do not reach the internal coat. A plexus of sympathetic 
nerves surrounds the vessels, and fibers from it are distributed to 
the muscular coat. 

Elasticity and Contractility of Arteries. — If an amount of 



l6o CIRCULATION. 

fluid corresponding to that of the " pulse volume " be suddenly- 
injected into the end of a rubber tube already distended with 
liquid the tube will be further distended or "pouched " by the 
injection, but will resume its former caliber if a correspond- 
ing amount of fluid be allowed to escape from the opposite 
end. This is, in a rough way, what happens to the arteries upon 
each ventricular systole. The pulse volume enters with much 
force the aorta (or pulmonary artery) in which the pressure is 
already high ; the artery is very elastic and expands under this 
influence, but immediately recoils with a greater pressure upon 
its contents. That pressure tends to force the blood along the 
vessel in both directions, but its return into the ventricle is 
effectually prevented by the now closed semilunar valves. Con- 
sequently it can go only toward the periphery. 

Now it is evident that the flow in the beginning of the aorta 
is intermittent ; but it is found that in vessels as large as the 
carotid and smaller the flow has assumed a remittent character, 
and that it approaches nearer and nearer to being continuous as 
the vessels become smaller, until that condition is established 
when the capillaries are reached. 

It is the elastic coat of the aorta which allows the vessel to 
expand and causes it to contract upon its contents forcing them 
onward. It is a force, superadded to that of the ventricle, in 
maintaining the circulation — a force derived from the ventricle, 
stored there to be used during diastole. It is, furthermore, in 
main part, this elasticity which accounts for the conversion of 
the intermittent into a remittent, and later a constant, flow. 
If the wall of the expanded aorta reacted upon the pulse volume 
with the same quickness and force as the ventricle and if the 
same kind of reaction characterized succeeding portions of the 
arterial tree, the blood would be handed from one segment to 
another without modification of the intermittency of its current. 
But the contraction of the vessel here is only a passive reaction, 
not due, like the heart's contraction, to the activity of striated 



ELASTICITY AND CONTRACTILITY. 101 

muscle, and takes place in a comparatively slow manner — last- 
ing, in fact until the next ventricular systole. The effect of the 
elastic tissue, then, in the very beginning of the aorta alone 
would tend to convert the flow into a continuous one ; when it 
is considered how the blood is handed on from segment to seg- 
ment of the arterial system, each possessed of elasticity, it is 
easy to see how the intermittency of the current is gradually ab- 
sorbed in its passage toward the periphery. It is also easy to 
see how more elastic tissue is needed in the large than in the 
small arteries. 

The function of the elastic coat is, therefore, twofold : (i) It 
forces the blood continuously toward the periphery \ (2) it is 
chiefly instrumental in changing the intermittent to a constant 
flow — a condition very necessary in the capillary system. 

The contractility of the medium and smallest arteries is resi- 
dent in their muscular coats ; and by the term ' l contractility ' ' 
here is not meant the passive reaction which follows distention. 
An inert rubber tube will react when distended, but has no 
inherent power of contractility, although it is usually said to 
"contract" under the condition just mentioned. The caliber 
of an artery in a normal state of tonicity may be one-twelfth 
inch, but by contraction of its muscular coat it may have a cali- 
ber of, say, one-twenty- fourth inch, or by relaxation of that coat 
a caliber of one-sixth inch— in both cases without any considera- 
tions of pressure inside it. 

This variation in caliber is just what is found frequently to 
take place. For it is evident that an organ requires different 
quantities of blood at different times, and the supply for the 
varying necessities is regulated through contraction or dilata- 
tion of the supplying vessel. For instance, more blood 
is needed in the alimentary canal during digestion, and the 
arteries going there are dilated. Less blood is needed in the 
glands in the intervals of secretion and the supplying vessels are 
contracted. Thus it is that the comparatively limited amount 



1 62 CIRCULATION. 

of blood in the body is distributed most abundantly to those 
parts in which, for the time, physiological activity is greatest. 
Of course the muscular tissue is under the control of the nervous 
system through the vaso-motor fibers. 

The prominent function, therefore, of the muscular coat is to 
regulate the supply of blood. 

Arterial Tension. — If a tube open at both ends have one end 
inserted into, say, the common carotid artery the blood will rise 
for a considerable distance in the tube and remain there. If a 
similar tube be inserted into the internal jugular vein of the 
opposite side (which, under the conditions, corresponds to the 
artery experimented upon) the height to which the blood rises 
in this tube will be much less than in the former one. This shows 
that blood exists in the arteries and veins under a certain degree 
of pressure, which is 8-9 times greater in the arteries than in 
the veins. 

Furthermore, the level of the blood in the tube connected 
with the artery shows a fluctuation, rising and falling regularly 
with respiration ; it also shows a less extensive, but more rapid, 
fluctuation with each heart beat, the highest point of this secon- 
dary rise being coincident in time with the ventricular systole ; 
the column falls then until the following systole. But at no time 
does the column in the arterial tube come near to being so low 
as that in the venous tube. 

The height of these columns is a measure of the different de- 
grees of pressure which sustain them, and obviously the height 
of the column will depend on the weight of the liquid used in 
the tube. Owing to the quick coagulability of the blood, the 
great amount of friction in so high a column and to other me- 
chanical difficulties which beset the experiment mentioned, an 
instrument, the mercurial manometer (the principle of which is 
the substitution of mercury for blood in the tube), has been de- 
vised to record with considerable accuracy the pressure in dif- 
ferent parts of the circulatory system. Hence it is that the 



ARTERIAL TENSION. 1 63 

blood pressure is usually given in terms of mercury. The aortic 
pressure in man is probably from 150 to 200 mm. (6-8 in.) of 
mercury. 

The Causes of Arterial Tension. — These are (1) friction 
in the vessels, (2) the incessant injection of the " pulse vol- 
ume " by the ventricle, and (3) the elasticity of the arterial 
walls. 

1. Of course there is an element of friction opposing the 
entrance of blood into the aorta from the ventricle ; but this 
resistance is relatively much greater in a small than a large tube, 
and is absolutely so when a number of small tubes represent the 
subdivisions of the large one. Consequently, the friction in the 
smallest vessels is, in the aggregate, enormously greater than in 
the aorta. It is, as it were, reflected from the capillaries toward 
the heart, constituting a constant and ever-increasing impediment 
to the onward current. 

2. There is a continuous escape of blood out of the arterial 
into the capillary system in spite of friction, and this would 
finally relieve the arterial tension were it not for the regular and 
frequent injection into the aorta of an amount of blood equaling 
that which has escaped into the capillaries since the previous 
systole. 

3. But if these two factors alone were concerned there 
would be no continuous pressure in the arteries; it would be in- 
termittent, and inoperative during diastole. The tube, how- 
ever, shows that the pressure is fairly constant, being only a little 
less during diastole than during systole. This is brought about 
by the elasticity of the arterial wall. 

The effect of the elastic wall on blood-pressure is illustrated 
by Howell as follows : Let it be supposed that, at the moment 
of observation, arterial tension has, for some reason, sunk very 
low, but that now a normal heart is forcing the usual amount of 
blood into the aorta. The first injection feels the influence of 
peripheral friction, and since the elastic wall is distended but 



164 CIRCULATION. 

slightly it meets with little resistance in expanding the wall to 
a degree necessary to accommodate that amount of blood ; it is 
easier to distend it than to overcome friction. Succeeding in- 
jections for a time will find it easier to distend the arteries than 
to overcome the peripheral resistance, but as each injection 
enters it makes room for itself with greater difficulty than did 
the preceding one, for the vessel becomes more and more diffi- 
cult to distend. Thus the pressure in the vessel becomes higher 
and higher, and as it does so it will become easier for a part of 
the contained blood to overcome friction and enter the capil- 
laries than to distend the wall. Finally the arterial wall will 
become so tense as to force into the capillaries, between two 
systoles, an amount of blood equal to that received by the first 
systole. The establishment of this equilibrium marks the resto- 
ration of normal arterial tension. 

It is seen that this force is operative during diastole as well as 
systole. When the ventricle forces a charge of blood into the 
aorta a large part of its energy is expended in distending the 
arterial wall ; it stores up a part of its energy thus to be dealt 
out while it rests in diastole \ that energy is dealt out by the 
recoil of the elastic wall, and this recoil, lasting until the suc- 
ceeding systole (and representing nothing but the prolonged 
action of the ventricle), exerts a continuous pressure upon the 
arterial contents and forces a continuous current toward the pe- 
riphery. 

Upon systole the arterial pressure rises, for the system of 
vessels must then accommodate more blood than at any other 
time ; during diastole the pressure steadily declines, because blood 
is escaping from the vessels through the capillaries and none is 
entering. At the end of diastole the pressure is least because 
the amount of blood in the arteries is at the minimum mark. 

It is apparent that, in reality, there are, under normal con- 
ditions, only two factors to be considered as controlling arterial 
tension — (1) the force of the left ventricle and (2) the resistance 



ARTERIAL TENSION. 165 

at the periphery. The elasticity of the arterial wall is only a 
means of storing up the energy of the ventricle. It furnishes a 
most striking example of the conservation of energy and the 
economy of its expenditure. When the amount of blood is 
constant arterial tension is chiefly governed by the condition of 
the capillaries and arterioles as to dilatation or contraction. 

The pressure in the pulmonary artery is considerably lower 
than in the aorta, but in general the remarks that have been 
made relative to the systemic circulation apply as well to the 
pulmonic. 

Pressure in Different Arteries. — The pressure is greater in the 
large than in the small arteries, but the difference is less than 
might be supposed. With an aortic pressure of 1 50 mm. the pres- 
sure in the metatarsal artery is something like 125 mm. When 
the proximity of the great outlet — the capillaries — to the small 
arteries and the increase in their combined capacity over that 
of the aorta is considered the reason for the diminution is appar- 
ent. 

Conditions Influencing Arterial Tension. — With normal ves- 
sels and a normal amount of blood the degree of tension will 
depend, as already intimated, usually on the action of the heart 
and the condition of the outlet. Anything increasing the 
amount of blood received without at the same time increasing the 
amount escaping will increase the tension ; the same result will 
obviously follow a normal intake and a decreased output. Op- 
posite effects will follow opposite conditions. In ordinary 
tranquil respiration arterial tension increases as a result of 
inspiration and decreases as a result of expiration. Mus- 
cular exercise increases it for the supposed reason that mus- 
cular contractions to some extent impede the entrance of 
blood into the capillaries, and for the further reason that dur- 
ing straining the chest is compressed and tends to force the 
blood out of the great vessels there. The effect of hemor- 
rhage on arterial tension needs no comment. Various emo- 




1 66 CIRCULATION. 

tional disturbances may diminish or augment the pressure through 

the nervous system. 

The Pulse. — By the term " pulse " is ordinarily understood 

the sudden incessant dilatations of the arteries corresponding to 

the incessant contractions of the heart. These periodic dilata- 
F tions depend, in point of fact, upon 

fluctuations in the arterial pressure, 
which fluctuations depend in turn upon 
the injection of blood from the heart, 
the elasticity of the arterial walls and 
the resistance of friction. Variations 

Tracing of Blood Pressure from the normal in any of these will 

taken with Fick's Mano- a i ter t h e character of the pulse. 

METER. {Yeo.) 

When the finger is applied to an 
artery a distinct sensation of enlargement is received just after 
each heart beat. But the increase in caliber is actually much 
less marked than the elongation of the vessel. 

If the radial and temporal, or better the radial and carotid, 
be palpated at the same time it will be discovered that the fluc- 
tuation due to any systole is recorded in the carotid earlier than 
in the radial, showing that an appreciable time is consumed in 
the passage of the wave from the beginning of the aorta to its 
peripheral divisions. It is estimated that the passage of the 
wave from the heart to the dorsalis pedis artery consumes about 
.2 second. 

It is not to be understood that the distention of any artery 
(except the very beginning of the aorta) is due to the passage 
through it of any part of the actual blood which entered the 
aorta at that systole which causes the pulse beat felt. It is only 
the transmission of the wave and not the body of the blood. 
The expansion of the arterial tree is a progressive one, passing 
from segment to segment in a peripheral direction. This pulse 
wave travels at the rate of from 10 to 30 ft., while the current 
itself seldom exceeds \y 2 ft. per second. 



THE PULSE. 



167 



Frequency and Regularity of the Beat. — These, of course, de- 
pend upon the frequency and regularity of the heart. Some 
conditions influencing these characteristics of cardiac action have 
been noticed. Sometimes, from either transitory or serious dis- 
orders, an otherwise regular pulse will omit a beat ; this signi- 
fies that the ventricle has missed a contraction in its regular time. 
Not always, however, does the peripheral pulse record the 
number of heart beats. Occasionally only every other beat, or 
less often every third beat, is of sufficient strength to cause a 
palpable pulse. 

Not a little information as to the condition of the heart and 
circulation, outside of frequency and regularity, can be obtained 
from the pulse ; and there have been distinguished the full- 



Fig. 38. 




Marey's Sphygmograph. 

The frame (B, B, B) is fastened to the wrist by the straps at B, B, and the rest of the 
instrument lies on the forearm. The end of the screw ( V) rests on the spring (R), the but- 
ton of which lies on the radial artery. Any motion of the button at R is communicated to 
V, which moves the lever (L) up and down. When in position, the blackened slip of glass 
(P) is made to move evenly by the clockwork {H) so that the writing point draws a record 
of the movements of the lever. ( Yeo. ) 

bounding, non-compressible, compressible, wiry, gaseous, thready 
and other kinds of pulse, they being supposed to give informa- 
tion as to the heart's action, or the peripheral resistance, or the 
condition of the vessel wall, or as to all of these. From me- 
chanical reasons which suggest themselves a ' ( large ' ' pulse often 
accompanies low tension, and a " small " pulse high tension. 



1 68 CIRCULATION. 

Pulse Tracings. — By means of the sphygmograph pulse trac- 
ings are taken (Fig. 38). The lever rises abruptly at the 
" pulse beat " and declines gradually until the next beat raises 
it ; thus it takes much longer for lever to fall than to rise. 

This instrument furnishes an accurate record of the varying 
arterial tension so far as the variations are due to individual 
contractions, and shows that, while the pressure declines in a 
general way throughout the whole period between pulse " beats " 
it does not do so in a uniform manner. At a certain short in- 
terval after the beginning of the decline the lever is interrupted 
temporarily and frequently even rises slightly again. The in- 
terpretation of this secondary rise of the lever is that a sec- 
ondary pressure wave is traversing the artery. This is called the 
dicrotic wave. Under normal circumstances it cannot be felt, 
but often in debilitated conditions when the pressure is low it 
can be detected by the finger ; it is then felt as a second smaller 
impulse quickly following the usual one, and, of course, in such 
case the dicrotic rise traced by the sphygmograph would be 
quite conspicuous. 

There is much discussion as to the origin of the dicrotic 
wave. Some hold that it is reflected like an echo from the 
peripheral friction and consequently travels centrally. This is 
hardly correct. It very probably results from a secondary im- 
pulse given to the blood column by the sudden closure of the 
semilunar valves at the end of systole and by the first 
quick recoil of the arterial wall upon its contents, the first 
(main) wave having been started by the sudden influx of blood 
at the beginning of systole when the artery is still expanding 
and the semilunar valves are still open. 

The condition of the muscular coat is not without its effect 
upon the pulse. It seems by its tonicity to prevent too great 
distention of the vessels. Relaxation of this coat, whether 
through nervous or other influence, such as external heat, causes 
a large, soft, compressible pulse, while contraction gives to it a 
small, hard, non-compressible character. 



THE CAPILLARIES. 1 69 

Rapidity of the Arterial Current. — This diminishes pro- 
gressively toward the periphery. In the carotid it has been esti- 
mated to have a velocity of 20 in. per sec. during ventricular 
systole, 8.5 in. during the passage of the dicrotic wave, and 
some 6 in. , as an average, between that wave and the next sys- 
tolic acceleration. For a mean carotid velocity of 10 in. per 
sec. the metatarsal velocity is probably a little over 2 in. The 
rate must be increased by relaxed arterioles and capillaries and 
retarded by contraction of these vessels. The decreased periph- 
eral rapidity is to be expected when the large relative capacity 
of the small vessels is remembered, though there are conditions, 
both local and general, which would invalidate any calculation 
based upon this circumstance alone. 

(C) The Capillary Circulation. 

Histology. — As the arteries progressively decrease in size it is 
found that those having a diameter of ^q- in. possess the three 
coats common to arteries in general, but that they are very thin ; 
when the diameter is reduced to -g-J-g- in. the external coat is 
lost, and the middle consists of a single layer of muscular fibers ; 
finally this coat is lost and only the thin homogeneous membrane 
lined with elongated endothelial cells remains. Anatomically, 
these last are the capillaries. 

The wall is elastic and may be contractile. The diameter 
(not the caliber) of the capillaries varies from 2 * ft to % q 0& in. 
They are smallest in nervous and muscular substance and largest 
in glands and the lungs. It is thus only the largest which 
will admit a blood corpuscle without change of shape. The 
wall is exceedingly thin. The average length of a capillary tube 
is about Jq in. Traced in either direction it is found to 
gradually assume the characteristics of either an arteriole or a 
venule. 

The capillaries form a true plexus, branching to form a most 
intricate network of tubes with no definite direction whatever, 



170 CIRCULATION. 

and with no change in diameter. They penetrate all the tissues 
of the body except the "non-vascular" such as the hair, nails, 
cornea, etc., which receive their nutrition by imbibition. No- 
where, however, do they penetrate the ultimate anatomical 
elements, such as gland cells, nerve fibers, etc. 

Fig. 39. 




Capillaries. 

The outlines of the nucleated endothelial cells with the cement blackened by the action of 
silver nitrate. (Landois.) 

Capacity. — The capacity of the capillary system is much 
larger than the arterial — probably five to eight hundred times. 

Physiologically, the capillaries begin where the interchange 
of materials between blood and tissue begins, and it is supposed 
that this interchange takes place only in the vessels which are 
designated capillaries from an anatomical standpoint. Except 
as regards their anatomy, the most striking characteristic of cir- 
culation in the capillaries is the fact that the current is no longer 
remittent but constant. 

The Capillary Flow. — A convenient and satisfactory situation 



THE CAPILLARY FLOW. 171 

in which to observe the phenomena of capillary circulation is 
the mesentery of the frog. It is scarcely possible .to make out 
the actual walls of the capillaries or of the small veins or ar- 
teries in the field, but only their profiles enclosing a current of 
passing corpuscles. In such a field are seen small vessels with 
several corpuscles abreast passing either at a steady rate or with 
rhythmical accelerations corresponding to the beats of the 
heart ; the former are venules ', the latter arterioles. 

In the capillaries the corpuscles usually pass in single file in a 
steady current, though dilatation often allows the passage of two 
or three abreast. The red corpuscles can seldom traverse a cap- 
illary without change of form. They are elongated so as to 
make one of their diameters much shorter than usual. They 
easily assume this shape, as a result of pressure, and as easily 
regain their normal outlines, when the pressure is removed. 

Not infrequently a corpuscle coming to a division of the 
channel is caught, distorted in shape, and finally, after oscillat- 
ing for a time, passes on in one of the currents open to it, re- 
gaining its form at once, or when it has passed into the larger ves- 
sel. In the capillaries the flow is slower than anywhere else. 
In one the current may be swifter than in another, and even in 
the same capillary the rate may be observed to vary, or a cur- 
rent in an opposite direction may be set up in a tube joining 
two others. It is to be remembered that the object of the capil- 
lary system is to spread the blood out, as it were, over a very 
large area so that it may be exposed freely to the cells ; and, 
while in the network as a whole there is a general tendency for 
the blood to pass from arterioles to venules, the plexus is so in- 
tricate and abundant that, except in capillaries connected directly 
with the larger vessels, it is not necessary for blood to pass in 
any one direction in any one capillary in order to ultimately 
reach the venous system. 

The corpuscles are seen not to come in contact as a rule with 
the confines of the tube, but to occupy the center of it only. In 



172 CIRCULATION. 

this space, between the corpuscles and the wall, is an inert 
layer of plasma, the ' ' still layer. ' ' When there are several cor- 
puscles abreast it may be observed that the more central ones 
move the more rapidly. This is because the friction is least 
there. This element of friction accounts for the still layer of 
plasma — the plasma being practically the only portion of the 
blood which will adhere to the wall. 

The leucocytes move largely in contact with the wall, and 
therefore progress much more slowly than do the red corpuscles. 
They roll over repeatedly in their passage and often stick to the 
side of the vessel for some time before being forced on by the 
current. Those seen in the main stream among the reds have a 
continual tendency to escape into the still layer and lag behind. 
This gravitation of leucocytes to the periphery of the current 
is said to be due to their relatively low specific gravity, as well 
as to the adhesive character of their surfaces. 

Rate of Capillary Flow. — Although the rapidity of the cur- 
rent varies in different parts of the tube, it is apparent that the 
capillary current is much slower than either the arterial or ven- 
ous ; and this is to be expected from the physical fact of the 
large relative capacity of the capillary system, and from the 
physiological fact that here must occur the interchange of ma- 
terials between blood and cells. It is of no little significance, 
too, that the flow here is constant, for such a circumstance cer- 
tainly enhances the even distribution and accession of materials. 
The average rate of flow in a capillary is thought to be from ^ 
to -g 1 ^- in. per second. If the length of the ordinary capillary is 
Jq in., it is seen that with this rate the time of any corpuscle in 
any capillary is exceedingly brief. 

Causes of the Capillary Circulation. — It is a fact not to be 
lost sight of that the cause of the whole circulation is the force 
of the ventricles. That force may not be exerted directly upon 
the circulating column, as when it is stored up in the elastic 
walls of the arteries to be dealt out during diastole ; or it may 



THE VEINS. 173 

be aided or inhibited by various circumstances, such as the 
valves of the veins, muscular contractions, respiration, etc.; but 
it is amply able to carry the current not only through the capil- 
laries, but through the veins back to the heart again. Its in- 
fluence is directly apparent in the pulse of the smallest arteries, 
and there is nothing in the phenomena of the capillary or 
venous circulation inconsistent with the transmission of its in- 
fluence to them. 

Pressure in the Capillaries. — The same forces which cause 
arterial pressure cause capillary pressure — (1) the hear? s action, 
(2) friction and (3) elasticity. The capillary walls have been 
said to be elastic ; they are continually in a distended condition 
from the continual reception of blood, and the reaction of their 
walls compresses their contents. The average capillary pressure 
is thought to be from 25 to 50 mm. of mercury. In depend- 
ent parts it is higher. That it is thus low is to be expected 
when the large capillary capacity is considered. Moreover, a 
very large part of the force of the heart has been used up in get- 
ting the blood out of the arterial system, and consequently less 
of it is available to distend the capillaries. 

(D) Venous Circulation. 

The veins exist for the purpose of getting the blood back to 
the heart. When it has traversed the systemic capillaries its 
function is performed until it is aerated again. The capillaries 
converge to vessels a little larger ; these are joined by other 
similar ones — all of which are the venous radicles, or venules. 
Uniting they form larger and larger vessels which, filled with 
dark blue venous blood, make their way toward the heart. The 
current here is more rapid as a rule than in the capillaries but 
less so than in the arteries, the capacity of the veins being about 
four times that of the arteries. Venous blood on its way to the 
heart (until it has entered the large vessels near that viscus) may 
go by more than one route since the veins present frequent an- 



174 CIRCULATION. 

astomoses. If the more direct route be blocked by muscular 
contraction or otherwise, the current may easily take a more cir- 
cuitous one. 

Histology. — The veins are thin and flabby as compared with 
the arteries. Their walls collapse on section. They possess 
three coats. 

The external coat is fibrous like that of the arteries ; near the 
heart are a few cardiac muscle fibers. The middle coat is 
chiefly composed of inelastic fibrous tissue ; it also contains some 
elastic fibers and non-striated muscular tissue. The internal 
coat is practically the same as in the arteries and capillaries ; the 
endothelial cells are less elongated. 

Thus it appears that while the vein wall is quite strong it pos- 
sesses neither much elasticity nor much contractility. Veins 
take very little active part in the circulation, and the strength 
of their walls would scarcely be necessary were the pressure 
evenly distributed as in the arteries. Vasa vasorum penetrate 
the middle coat. 

Valves of the Veins. — At frequent intervals in the course of 
all veins except very small ones and those in the large cavities 
are small folds protruding into the lumen known as the venous 
valves. They are quite firmly fixed, in pairs usually, and pre- 
vent a backward flow of the blood. They can be readily demon- 
strated in the extremities by rubbing the skin distally, when 
they produce, by the obstruction which they offer, knotted ap- 
pearances in the venous column. 

Venous Current. — The flow of blood in the veins shows 
nothing of the rhythmical accelerations evident in the arteries. 
It is more sluggish, and, other things being equal, the rapidity 
is directly dependent upon the rate at which blood is supplied 
by the capillaries. But the current cannot be uniform ; it is 
often interrupted by a contracting muscle or pressure from some 
other cause, in which case the valves prevent regurgitation 
and the blood must seek another way to the heart. Different 



VENOUS PRESSURE. 



175 



routes are made possible by the anastomoses. Distention from 
any reason naturally causes the vessel to react upon its contents 
and force them into whatever channel will admit them. Occa- 
sionally when a gland is particularly active and its supplying 
vessels are therefore dilated, the pulse may be transmitted to 

the venules. 

Fig. 40. 




A, vein with valves open, b, with valves closed ; stream of blood passing off by lateral 
channel. (Kirkes after Dalton.) 

The speed of the venous current, in the long run, must de- 
pend upon the total capacity of the vessels. No estimate for 
the rapidity in any one part will answer for all parts or for the 
same part at all times. The current is more rapid near the 
heart than toward the periphery. 

Venous Pressure. — From what has been said it is evident that 
venous pressure is very inconstant. In the small veins it is 
lower than in the capillaries, and it diminishes as the heart is 
approached. Any circumstance favoring the flow from the 
capillaries increases it. It is usually high when the arterial pres- 



176 CIRCULATION. 

sure is low and vice versa. During inspiration it is lessened in 
the large veins near the heart, and falls below the atmospheric 
pressure, so that the opening of one of these vessels is very dan- 
gerous lest air be sucked into the vein and reach the heart. 

Causes of the Venous Flow. — The one great cause is the 
ventricular contraction. Superadded to this are several others. 
Muscular contractions (in connection with the valves) serve to 
aid the venous circulation provided they are intermittent. The 
muscles compress the veins, and, since the valves prevent regur- 
gitation, the blood is obliged to go toward the heart ; if now 
the muscle relax the vein will fill again, and if another contrac- 
tion follow the same performance will be repeated. The value 
of this force is well illustrated in the fact that varicose veins of 
the lower extremities occur much less often in connection with 
occupations which require walking than when simple standing 
is necessary. Gravity aids in case of those veins whose course 
is downward. Aspiration of the thorax aids by its " suction " 
force. The power of muscular contraction is also possessed in 
some degree by the veins. 

Pulmonary Circulation. — The remarks made concerning the 
systemic circulation apply in general to the pulmonary, but it is 
to be remembered that in this case the arteries contain venous 
and the veins arterial blood. The circuit is much shorter and 
the capillary resistance is less ; consequently it is not surprising 
that the force of the right ventricle is much below that of the left 
— about one-third as great — and that the wall of the pulmonary 
artery is thinner than that of the aorta. The course of the 
blood is from the right ventricle to the left auricle. 

The Rapidity of the Entire Circulation. — So far as possible 
the rate of the flow in the three systems of vessels has been 
given. When a properly colored fluid is injected into the jugu- 
lar vein, whence it passes through the heart, the pulmonary cir- 
culation, the heart a second time and thence into the systemic 
circulation of the head back to the starting point (or to the op- 



VASOMOTOR NERVES. I 77 

posite jugular vein), the time occupied in this circuit is about 21 
sec. From this it is estimated that, for the general system 
(where the average route is longer), some 23 sec. are consumed 
in the passage of any part of the blood through the entire cir- 
culatory apparatus. 

Increase of the cardiac rate increases slightly the rapidity of 
the blood current when the increased rate is due to physiolog- 
ical causes, such as muscular exercise \ the current is probably 
diminished in rapidity when the cardiac rate is increased from 
pathological causes, such as fever. 

Innervation of the Blood-vessels. — Frequent reference has 
been made to the contraction and relaxation of the muscular 
coats of the vessels. These movements are under the control of 
the vaso-motor nerves, the term vaso-motor including both vaso- 
constrictor and vaso-dilator nerves. They are present in the 
veins as well as in the arteries. Stimulation of the vaso-constric- 
tors lessens the vessel's caliber \ stimulation of the vaso-dilators 
increases it. 

Both kinds of fibers are often found in the same nerve trunk, 
as in many branches of the sympathetic or in the sciatic. Stim- 
ulation of such a trunk causes constriction of the vessels to which 
its vaso-motor fibers are distributed because the vaso-dilators are 
less easily irritated than the vaso-constrictors. Section of a 
trunk containing them causes dilatation of the vessels they supply 
since the " tonic " influence of the vaso-constrictors is removed. 

The origin and course of the vaso- motor nerves has been a 
subject of very great confusion among writers. The following 
facts are given for the supposed truth : The vaso-motor fibers 
reaching the vessels proceed from cells in the sympathetic ga?tglia i 
but these cells are influenced by cells in the vaso-motor centers. 
The chief vaso-motor center is in the medulla ; subordinate 
centers exist in the cord, probably in the cells of the anterior 
cornua. Fibers from the bulbar center pass in part to the nuclei 
of origin of the cranial nerves, but mainly to the subordinate 



178 CIRCULATION. 

cord centers. Fibers from these last named pass out with the 
anterior spinal roots to end in arborizations around the vaso- 
motor cells of the sympathetic ganglia. Thus the vaso-motor 
nerves are considered as belonging to the sympathetic system ; 
but it must not be supposed that they are not found running in 
cerebro-spinal trunks. Such a circumstance, however, is only a 
matter of expediency and has nothing to do with the character 
of their action. There seems no doubt that the axis-cylinders 
of all the spinal vaso-motor cells pass to sympathetic ganglion 
cells \ so that when it is said, for instance, that the vaso-motor 
fibers for certain parts pass out of the cord by the anterior roots 
of the third, fourth and fifth lumbar nerves, it is not meant that 
these fibers are themselves distributed to the vessels : they end 
by arborizing around sympathetic ganglion cells, whence fibers 
pass to the parts in question. The vaso -dilators differ from the 
vaso- constrictors in passing directly through the ganglia of the 
sympathetic chain, and have their cell stations farther on, or 
even in the vessel wall itself. 

Vaso-motor reflexes occur from impressions conveyed either 
from the vessels themselves or from the general sensory surface. 
The latter is much the more common way. Usually the reflex 
constriction or dilatation is confined to the area of the nerve 
stimulated, but sometimes this is not so. When the vessels of 
one hand are contracted by its being thrown into cold water, 
those of the opposite hand are similarly affected. It seems that 
the vaso-motor nerves have the power to bala?ice the circulation 
in different parts ; when the superficial vessels are dilated the 
deep are contracted and vice versa ; when the abdominal vessels 
are dilated during digestion the superficial are contracted, etc. 
Sudden flushes or pallor of countenance are good examples of 
vaso-motor action, impressions being carried from the cortex 
(if an emotion be the cause) to the bulbar vaso-motor center. 

It is unnecessary to give examples of vaso-motor action since 
they are constantly referred to. When it is remembered that 



THE BLOOD. 1 79 

the entire physiological distribution of the blood is regulated by 
these fibers their importance is apparent. It is by their action 
that the blood flow is increased to the gastro-intestinal tract dur- 
ing digestion, to all glands during their activity, to muscles dur- 
ing exercise, and to all parts where physiological activity is in 
progress. It is by them also that the blood flow is decreased 
to parts when occasion demands a less amount. 

(II) THE BLOOD. 

Functions. — The office of the blood is to carry to the tissues 
nutritive materials resulting from digestion and oxygen from the 
lungs, to convey away from the tissues to the several organs of 
excretion the broken-down products of physiological activity, 
to convey internal secretions from one part of the body to an- 
other, and to aid in the equalization of temperature. It is there- 
fore immediately necessary to life — indeed to the life of every 
cell in the body, and, with the exception of such extravascular 
tissues as cartilage, nails, etc., which receive their supply from 
neighboring tissues, it supplies nutriment directly to all the cells 
of the organism. 

Amount of Blood. — It has been estimated that the total 
amount of blood in the average man is about 8 per cent., or one- 
twelfth, of his body weight. At all times something over 80 per 
cent, of this amount is contained in the liver, muscles, heart and 
lungs. The liver contains more than the resting muscles. 

General Properties. — The blood is an opaque fluid of a faint 
characteristic odor, salty taste, and alkaline reaction. Its aver- 
age specific gravity is 1055. It is warmest in the hepatic veins 
where it has a temperature of about 107 ° F. In the peripheral 
vessels its temperature is about 99 °, while in the deeper ves- 
sels in general it probably varies from ioo° to 107 °. The 
color of arterial blood is bright red ; that of venous blood, ex- 
cept when coming from actively secreting glands, is almost 
black. Plasma, free from corpuscles, is clear and it is, there- 



I50 CIRCULATION. 

fore, the corpuscles which give the blood its color. The pres- 
ence of oxygen in the red corpuscles accounts for the red color 
of arterial blood. When the oxygen is lost in the capillaries 
the change to the venous color takes place. It is the absence of 
oxygen, not the presence of carbon dioxide, which accounts for 
the color of venous blood.- 

Histological Elements. — The blood is composed of (i) a 
clear fluid, the plasma, or liquor sanguinis, and (2) three kinds 
of corpuscles — the red, the white or leucocytes, and the blood- 
plaques or platelets. The bulk of plasma to that of corpuscles 
is probably about 2 to 1, though it is sometimes given as being 
only a little greater than that of the corpuscular elements. 



Fig. 41. 



A 







c 

c 




aj 


1 


IN. ^^- — 


r- „!T>^ */\ 



A, human colored blood-corpuscles — i, on the flat; 2, on edge; 3, rouleau of colored cor- 
puscles. B, amphibian colored blood-corpuscles — 1, on the flat: 2, on edge. C, ideal trans- 
verse section of a human colored blood-corpuscle magnified 5,000 times linear — a, b, diameter ; 
c, d, thickness. (Landois.) 

RED CORPUSCLES. — These are biconcave circular disks hav- 
ing a diameter of about -g^V o m - Tne y probably vary less in size 
and shape than any other anatomical element in the body and 
are consequently taken as a standard of measurement for other 



THE BLOOD. 151 

structures. They are organized nitrogenous bodies containing 
also inorganic and organic non-nitrogenized materials. Their 
elasticity has been referred to in describing their circulation. 
Their specific gravity is about 1088. The biconcave surfaces 
cause it to appear that they have dark borders when the centers 
are in focus and dark centers when the borders are in focus ; 
but this is only because the two portions cannot be in focus at 
the same time. They present a bright yellow appearance when 
seen in comparatively small numbers, as under the microscope, 
the red color being evident only when they are seen in mass. 

In shed blood the red corpuscles show a decided tendency to 
accumulate surface to surface like coins of money to form rou- 
leaux. This results from a post mortem exudate upon their sur- 
faces. On exposure to the air they quickly shrink, presenting 
a peculiar characteristic appearance, and are said to be crenated. 
They have no limiting membrane and no nucleus. In the 
human male they exist to the number of about 5,000,000 per 
cu, mm. of blood; in the female the number is. about 4,500,- 
000. There are supposed to be some 25,000,000,000,000 in 
the human body. There is a significant and " compensatory " 
increase in the number at high altitudes where the atmosphere 
is rare. The biconcave surfaces increase the area for exposure 
to oxygen. 

Function of the Red Corpuscles. — It is the plasma which is 
concerned in conveying nutrition to the cells except so far as 
oxygen is concerned. It is the function of the red corpuscles 
to convey this gas from the lungs to the tissues. This may 
be said to be their only function ; while they do carry away 
some carbon dioxide from the cells, it is chiefly the plasma 
which is the vehicle of this gas. The function of carrying oxy- 
gen is altogether dependent upon the presence of hemoglobin, 
and a consideration of this substance will practically include 
the function of the red corpuscles. 

Hemoglobin. — This is the coloring matter of the blood. The 



1 82 CIRCULATION. 

red corpuscle consists of a skeleton of supporting network, very 
delicate in structure, known as the stroma , and of hemoglobin. 
The latter constitutes the bulk of the corpuscle, forming some 
95 per cent, of the solid matter. It is of proteid composition, 
and may be decomposed into globin, hematin and an unknown 
residue. It is thought to consist of carbon, hydrogen, oxygen, 
nitrogen, iron and sulphur. It is present in human blood to 
the extent of from 125 to 150 parts per thousand. Its peculiar 
property is that of combining with oxygen to form oxyhemo- 
globin whenever it is exposed to that gas. Oxyhemoglobin is quite 
unstable. It readily gives off oxygen when placed in an atmos- 
phere devoid of oxygen, or when the oxygen pressure is dimin- 
ished — a condition which is shown under Respiration to exist 
in the capillaries. The hemoglobin left after oxygen has been 
given up is known as reduced hemoglobin. 

Any gas for which hemoglobin has a stronger affinity than 
for oxygen will, if present, of course, take the place of oxygen 
and prevent the formation of oxyhemoglobin. Carbon monox- 
ide or nitrous oxide will do this. The former causes asphyxia 
when ordinary illuminating gas is inhaled, because it forms with 
hemoglobin a relatively stable compound, carbon -monoxide- 
hemoglobin, which is not broken up in the capillaries and 
which, if it were, would not furnish the necessary oxygen to the 
cells. It poisons because it prevents the appropriation of oxy- 
gen by the hemoglobin. 

It is claimed that the small part of carbon dioxide which is 
conveyed away from the cells by the red corpuscles is also in 
combination with hemoglobin. The idea has been advanced 
that the oxygen combines with the pigment portion and the 
carbon dioxide with the proteid portion of hemoglobin. 

The presence of iron in hemoglobin seems to be requisite to 
the formation of oxyhemoglobin. It exists in very small amount, 
but is essential. It is not free, but constitutes a part of the 
molecular formula of hemoglobin. It clings to the hematin 
molecule upon dissociation. 



THE BLOOD. 1 83 

Hemoglobin is supposed to be the origin of the bile and 
urinary pigments. 

Development and Fate of the Red Corpuscles.— The average 
life of a red corpuscle is probably not very long. Their con- 
tinued destruction is an accepted fact, and this necessitates their 
continual manufacture. In a human adult the red corpuscles 
are formed in the red marrow of bone. In the embryo they 
are formed elsewhere, but by no special organs before the osseous 
system develops. When rapid manufacture is called for, as af- 
ter hemorrhage or as a consequence of other pathological condi- 
tions, the red marrow is greatly stimulated in respect to this 
function, and not infrequently the corpuscles appear in the cir- 
culation before they have lost their nuclei — a circumstance 
which under normal conditions does not occur. Is has not been 
shown that the spleen is concerned in forming red corpuscles. 

As to the destruction of these elements, it is probable that this 
takes place in any part of the circulation without the interven- 
tion of any special organ, the pigment being carried to the liver 
and kidneys and there discharged in the bile and urine. There 
is some evidence that the spleen and liver are particularly con- 
cerned in this destruction, but the proof is by no means conclu- 
sive. 

WHITE CORPUSCLES. — The white corpuscles, or leuco- 
cytes, are granular in appearance, have an average diameter of 
y^q-q in. and no characteristic shape. Their number varies with 
many conditions, but probably averages some 7,500 per cu, mm. 
of blood. Their surfaces have a more adhesive character than do 
those of the red corpuscles. Their appearance is indicated by 
their name. They are found under normal conditions in the 
blood, lymph, chyle, and other fluids of the body. Pus cells 
are dead leucocytes, and leucocytes are found to be increased in 
number in the blood during ordinary inflammatory processes. 
They are also more numerous during digestion than in the in- 
tervals. 



184 



CIRCULATION. 



According to their staining properties, their size and the shape 
of their nuclei they are divided into polymorphonuclear, large mono- 
nuclear, small 'mononuclear , eosinophile and transitional leucocytes. 
This division is of significance in many pathological conditions. 
Their most striking property is that of ameboid movement, and 
it is chiefly through the exercise of it that they perform their 

physiological duties. 

Fig. 42. 




Human Leucocytes Showing Ameboid Movements. {Landois.) 

Functions of the Leucocytes. — Howell gives to the leuco- 
cytes a five -fold function. (1) They ingest pathogenic bacteria 
and thus protect the body from these organisms. (2) They aid 
in the absorption of fats from the intestine. (3^ They aid in 
the absorption of peptones from the intestine. (4) They are con- 
cerned in blood coagulation. (5) They help to maintain the 
proper amount of proteid in the plasnia. 

With respect to (2) and (3), it should be said that reference 
is had to leucocytes in the submucous lymphoid tissue of the 
alimentary canal rather than to those in the blood current during 
the absorptive act. As regards (5), it is thought that the leu- 
cocytes continually undergo disintegration in the current, and 
the products of the process may keep up the normal amount of 
proteid in the plasma. 



THE BLOOD. 185 

Origin of Leucocytes. — These corpuscles increase by cell 
division in the current ; their ultimate origin in the adult is 
probably in most part from the spleen and lymphoid tissue through- 
out the body, whence they reach the blood by the lymph stream. 
It is not impossible that the red marrow is also productive of 
leucocytes. In fetal life these are developed without the inter- 
vention of any special organ. 

BLOOD PLATELETS. — These are formed elements in the 
blood, have one-sixth the diameter of the red corpuscles, and their 
proportion to these latter is about i to 20. There is no evidence 
that they develop into corpuscles. It is not impossible that 
they are the nuclei, whole or broken up, of disintegrating leuco- 
cytes. They take part in coagulation. 

Composition of the Blood. — The blood, as a whole, contains 
of water about 790 parts, the remainder being organic and inor- 
ganic solids. The inorganic salts constitute only some 8 parts 
per thousand ; they are principally those of sodium, calcium, 
magnesium and potassium. 

Composition of the Corpuscles. — The red corpuscles contain 
about 680 parts water, 310 parts organic and 10 parts inorganic 
solids. The most important of the organic solids is hemoglobin, 
which constitutes about 95 per cent, of these. Besides hemo- 
globin there are other proteid materials, mainly globulin and 
fatty matters, such as lecithin and cholesterin. The corpus 
cles contain an excess of potassium salts and a deficit of sodium 
salts as compared with the plasma. The properties of hemoglo- 
bin have been referred to. 

' The composition of the white corpuscle is doubtful. Their 
proteid is probably nuclein. They also contain lecithin, cho- 
lesterin and glycogen together with inorganic salts. 

Nothing is known of the composition of the blood-plaques. 

The Blood Plasma. — The plasma in a thin layer is perfectly 
colorless, but in quantity has a clear yellowish tinge from the 
presence" of some unknown pigment. Its specific gravity is 



1 86 CIRCULATION. 

about 1028. The plasma is not identical with the serum as will 
be seen under the discussion of coagulation. 

Composition of the Plasma. — When we remember that the 
blood is analogous to the tissues in that it contains organized 
cells requiring nutriment and throwing off wastes, and that it 
furnishes nutriment to all parts of the body and removes the 
products of their disassimilation, we have already an idea as to 
what things it contains. In a general way it may be said that 
the corpuscles and plasma contain the same materials, but in 
widely varying proportions. A discrepancy in the salts of 
sodium and potassium has been mentioned ; the phosphorized 
fats are relatively abundant in the corpuscles while the fatty 
acids predominate in the plasma. Briefly, the plasma contains 
in 1,000 parts, 920 of water and 80 of solids; of the solids 70 
are organic and 10 are excrementitious and inorganic salts. 

Flint classifies the constituents of the plasma, and of the en- 
tire organism, as (1) inorganic, (2) organic saline, (3) organic 
non-nitrogenized, (4) excrementitious and (5) organic-nitrog- 
enized. 

1. The inorganic constituents need no special reference. 
They belong to the binary class of proximate principles, and 
pass through the system unchanged. 

2. The organic saline constituents belong to the ternary class 
of proximate principles. They are formed in the body, the lac- 
tates being a typical example ; these probably result from a union 
of lactic acid (resulting from changes in the dextrose of the 
blood) with a base from the decomposition of bicarbonates. The 
union of fatty acids with bases is another example of this class. 

3. The organic non-nitrogenized constituents are derived from 
the food, but do not exist in the blood in large quantity. They 
belong to the ternary class of proximate principles, and repre- 
sent the oleaginous and saccharine foods. 

4. The excrementitious materials are chiefly carbon dioxide, 
urea, urates, creatin, leucin, tyrosin, xanthin, etc. They will 
be noticed under Excretion. 



THE BLOOD. 1 87 

5. The nitrogenized constituents correspond to the quaternary 
class of proximate principles and are the most important in the 
plasma. The three chief of these are serum albumin, serum glob- 
ulin (paraglobulin) and fibrinogen. 

Serum-albumin is supposed to be the form assumed by the 
largest part of the peptones in the blood ; they seemingly 
undergo a change in being absorbed and appear in the blood 
chiefly as serum-albumin. This substance is supposed to furnish 
the bulk of proteid nourishment to the cells, it, like the other 
nutritive materials, being passed from the blood to the lymph 
and thence to the cells. It is probably identical with " serine," 
and exists in blood to the extent of some 53 parts per thousand. 

Paraglobulin, or serum globulin, has an obscure origin. It is 
natural to suppose that it comes from digested proteids, and this 
is probably correct. There is some evidence that it comes from 
disintegrated leucocytes. It doubtless contributes to the pro- 
teid demands of the cells, but whether it is appropriated as 
serum -globulin or changed to some other form is not determined. 

Fibrinogen also has an obscure origin and function. It is 
directly concerned in coagulation, giving rise to fibrin in a way 
to be described presently ; but it is not known what nutritive 
office it may have. It has been suggested that its origin is in 
the disintegrating leucocytes. It constitutes about 3 parts in 
one thousand of the blood. 

These three constitute the main proteid substances of the 
plasma ; though others are mentioned they are usually these 
same substances under different names or supposed constituent 
parts of these. Fibrinogen and paraglobulin are said by some 
to exist together under the name of plasmine. 

Coagulation of Blood. — The clotting of shed blood is a 
matter of common observation. It is of prime importance in 
the checking of hemorrhage. When blood is received into a 
vessel it soon assumes a jelly-like consistence, and later the 
mass becomes firmer and smaller. There is pressed out of it a 



1 88 CIRCULATION. 

fluid very like plasma in appearance called blood serum, which 
accumulates on the top of the clot owing to its relatively low 
specific gravity. 

The essential part of the clotting process is the formation of 
fibrin. As soon as the blood is drawn, unless the containing 
vessel be shaken, or the fluid agitated in some other way, the 
corpuscles sink toward the bottom and are caught in the meshes 
of the fibrin as it forms. The fibrin is deposited in the shape 
of fine fibrils interlacing to make a close network. Fibrin con- 
tracts when it has been formed, and thus it is that the serum is 
forced out. The inclusion of the red corpuscles, and conse- 
quently the red appearance of the clot, is only an accident ; 
they remain a part of the clot only because the contraction of 
the fibrin cannot force them out as it does the serum ; their 
presence is not necessary to coagulation. 

The explanation of coagulation resolves itself into an explan- 
ation of the formation of fibrin. There is at present no abso- 
lutely satisfactory explanation of the process. Probably the 
most widely accepted view is that after blood is shed there is 
formed from the disintegrating leucocytes a substance called 
fibrin ferment, which ferment unites with fibrinogen to form 
fibrin. The fibrinogen and fibrin ferment are called " fibrin fac- 
tors." Fibrin ferment does not exist in the circulating blood 
— at least not in sufficient quantity to cause coagulation. More- 
over it has become evident that clotting will not occur without 
the presence of calcium salts, though in what way they influence 
the process is not known. 

When blood clots the destruction of leucocytes must precede. 
This may be caused in the vessels by the introduction of foreign 
bodies into the current, or by injury to the lining epithelium of 
the tube. Blood does not clot in the vessels under normal con- 
ditions because not enough leucocytes disintegrate to form the 
necessary amount of fibrin ferment. 

The serum is the plasma minus the fibrin. 



THE LYMPH. 1 89 

The relation of plasma, serum and clot is shown by the ac- 
companying schema. 

1-d, f Serum 

Plasma { Fibrin . 

Corpuscles 

THE LYMPH. 

The lymph is a clear colorless fluid contained in the lymphatic 
vessels and tissue spaces. It resembles plasma in general ap- 
pearance and does not differ greatly from it in composition. 

The Lymph Vessels. — These vessels originate in at least 
three different ways, (i) All cells may be said to be bathed 
in lymph, being surrounded by that fluid lying in the irregu- 
larly shaped spaces between them. These spaces communi- 
cate with each other and finally converge to the lymph capil- 
laries. The intervals are called the " extravascular lymph 
spaces" (2) In certain situations, particularly in the nervous 
centers, the small blood-vessels are completely surrounded by 
and included in larger tubes, the ' 'perivascular lymph canals. ' ' 
These likewise pass on* to the lymph capillaries proper. (3) 
The large serous cavities, like those lined by the peritoneum, 
pleura, tunica vaginalis, etc., have large numbers of lymphatic 
radicles opening abruptly into them, or rather originating from 
them, and these may be considered as great extravascular lymph 
spaces. 

The course of the lymph is from the tissues to the subclavian 
veins, where it enters the vascular circulation. The lymphatic 
vessels from the right arm and the right side of the face, head and 
chest converge to form the ductus lymphaticus dexter, which 
enters the right subclavian vein at its junction with the internal 
jugular. The lymphatics from all other parts of the body con- 
verge to form the thoracic duct, which enters the left subclavian 
vein at its junction with the internal jugular. The thoracic 
duct begins by a dilated pouch lying upon the second lumbar 



190 



CIRCULATION. 



Fig. 43. 




Diagram Showing the Course of the Main Trunks of the Absorbent System. 



The lymphatics of lower extremities, D, meet the lacteals of intestines, LAC, at the recep- 
taculum chyli, R.C., where the thoracic duct begins. The superficial vessels are shown in 
the diagram on the right arm and leg, S, and the deeper ones on the left arm, D. The glands 
are here and there shown in groups. The small right duct opens into the veins on the right 
side. The thoracic duct opens into the union of the great veins of the left side of the neck, 
T. (Veo.) 



THE LYMPH. I9.I 

vertebra. This pouch receives the 1-4 lymphatic branches 
which have converged from the lacteals, and is called the recep- 
taculum chyli. The lacteals pass through the mesenteric lym- 
phatic glands on their way to the receptaculum chyli. 

The distribution of the lymphatics needs no comment when 
it is known that they receive the plasma which has been passed 
out of the vascular capillaries and thus collect fluid from well- 
nigh every tissue in the body. 

The structure of the lymphatics is quite similar to that of the 
veins, though they are more delicate. The lymph capillaries 
probably contain only a single coat like the venous capillaries. 
In the large vessels this thin endothelial coat is supplemented by 
connective tissue fibers together with some elastic and non- 
striated muscle fibers. They are very abundantly supplied with 
valves which operate in the same way as the venous valves. 
The vessel wall is quite elastic and has some contractile power. 

Lymphatic Glands. — All the lymphatics pass through one or 
more lymphatic glands on their way to the larger trunks. These 
bodies are not true glands. Their structure is adenoid. There 
are some six or seven hundred in the body, varying in size from 
a pinhead to a large bean. The superficial glands are especially 
abundant about the groin, axilla, neck and the other flexures. 
The deep ones are most numerous about the great vessels. The 
mesenteric glands are found between the folds of the mesentery. 

The lymphatic glands are of irregular shape and contain within 
their substance large numbers of lymph spaces or canals through 
which the incoming lymph must pass. The vasa efferentia are 
usually fewer in number and larger in size than the vasa affer- 
cntia. The current must be considerably delayed in the glands. 
They are probably concerned in the elaboration of leucocytes 
of the lymphatic circulation, while their retention of toxic ma- 
terials — even to their own hurt — is a common pathological oc- 
currence. 

Properties and Composition of Lymph. — Lymph is a com- 



I92 CIRCULATION. 

paratively clear liquid containing leucocytes. After meals the 
color becomes whitish from the admixture of chyle, and nu- 
merous fat droplets are present. Neither red corpuscles nor 
platelets are thought to be found in lymph except accidentally. 
The specific gravity is lower than that of the blood. Lymph 
coagulates when drawn, since the fibrin factors are present ; but 
the process is less prompt and the clot is less firm than in case 
of blood. 

In order to form an idea as to the constituents of lymph it is 
only necessary to say that its ultimate origin is the blood plasma, 
except in so far as its composition is changed during digestion. 
The plasma makes its way through the capillary walls out to 
the tissues bringing nourishment to them and removing waste 
products from them. In thus coming in contact with the tis- 
sues the plasma finds itself in the extravascular lymph spaces and 
its name is simply changed to lymph. It thus appears that 
lymph may enter the extravascular spaces by the direct passage 
of plasma out of the vessels or by being excreted, as it were, 
from the tissue cells. 

In any case the constituents of lymph are not very differ- 
ent from those of plasma, except, of course, when intestinal 
digestion is in progress and chyle is introduced into the lym- 
phatic circulation. It contains the three plasma proteids, urea, 
fat, lecithin, cholesterin, sugar and inorganic salts. The proteids 
are less abundant than in plasma, as might be supposed when it 
is remembered that they possess little osmotic power. The 
inorganic salts are in about the same proportion in both fluids. 
It is significant that the amount of urea and related excre- 
mentitious products is more abundant in lymph than in plasma ; 
their source is the destructive metabolism going on in the cells 
to which the plasma has been supplied, this plasma finding 
its way back as lymph. It is by no means certain, however, 
that all the plasma escaping from the capillaries is carried away 
by the lymphatic system. Some may reenter the blood-vessels. 



THE LYMPH. 1 93 

There is no unanimity of opinion as to the exact method of 
passage of plasma through the capillary walls into the lymph 
spaces. Some maintain that the phenomena can be explained 
by the ordinary physical laws of diffusion, filtration and osmosis 
when existing conditions of pressure, etc., are taken into consid- 
eration. Others hold that these laws are insufficient in them- 
selves to account for various occurrences in this connection, and 
ascribe to the capillary endothelium some active secretory power 
governing, or at least influencing, the outward passage of the 
plasma. 

The Flow of Lymph.— There is no organ corresponding to 
the heart to keep the lymph current in motion. The main causes 
for its direction from the extravascuiar spaces toward the veins 
in the neck is the degree of pressure to which it is subjected in 
those spaces as compared with the inferior, or even " negative," 
pressure obtaining near the terminations of the great ducts. It is 
known that at all times the venous pressure in the subclavian veins 
is low and that it may even fall below the atmospheric pressure, 
so that "suction" is exerted upon the lymphatic ducts where 
they enter those vessels. The lymph pressure in the extravas- 
cuiar spaces is estimated to be one-half the capillary blood-pres- 
sure. Friction and gravity (where the course of the vessels is 
upward) oppose the passage of the fluid. Consequently it accu- 
mulates in the spaces and in the smaller lymphatics until the 
pressure there becomes greater than the resistance of these forces, 
when it passes onward. Since lymph is being continually pro- 
duced this superior pressure in the extravascuiar spaces and small 
lymphatics is a fairly constant factor and keeps up a correspond- 
ingly constant current. 

There are two factors which are accessory to this peripheral 
pressure : (1) Thoracic aspiration by bringing about negative 
pressure in the veins in and near the chest brings about a like 
condition in the tributary lymphatic ducts ; furthermore, the 
effect of aspiration makes itself felt directly upon the thoracic 
13 



194 CIRCULATION. 

duct since its greatest extent is in the thorax. (2) The valves 
of the lymphatics act in a similar manner to those of the veins 
and constitute a very necessary factor in the lymphatic circula- 
tion. Although the lymph flow resembles that of the venous 
blood, it is less regular and more sluggish, but probably not 
so slow as might be supposed. Properly colored solutions in- 
jected into the blood have been demonstrated in the lymph of 
the thoracic duct " in from four to seven minutes." 

Lymph and Chyle. — It is scarcely necessary to refer to the 
differences between these two fluids. Chyle is the intestinal 
lymph during digestion. In the intervals of digestion the con- 
tents of the lacteals do not differ materially from lymph in 
other localities. Chyle has a whitish milky appearance due to 
the presence of emulsified and saponified fats. Its specific grav- 
ity naturally depends largely upon the amount of fat ingested, 
but is always higher than that of ordinary lymph and lower than 
that of blood. Not only is there more fat in the chyle than in 
lymph, but the other solids are also increased. The proteid 
constituents are considerably more abundant. For the most part 
the higher specific gravity is explained by the absorption of 
solids in solution from the alimentary canal. 

Chyle is forced out of the lacteal by contraction of the non- 
striated muscle fibers which run along by the vessel. When re- 
laxation of the fibers occurs, return of chyle into the lacteal is 
prevented by a valve at the base of the villus. 



CHAPTER VI. 
RESPIRATION. 



Object. — The object of respiration is to furnish oxygen to 
the tissues and remove carbon dioxide from them. The inter- 
vention of the lungs and blood is necessary to accomplish this 
end. At each inspiration a certain volume of air is taken into 
the lungs, and from it, while in these organs, is removed a cer- 
tain amount of oxygen which enters the blood of the pulmo- 
nary capillaries. At each expiration there is removed from the 
lungs a certain volume of air, and it contains a proportion of 
carbon dioxide over and above that contained in the ordinary 
atmosphere, i. e., in the inspired air ; this carbon dioxide is re- 
moved from the blood of the pulmonary capillaries and enters 
the air in the lungs. The entrance and exit of air to and from 
the lungs, in obedience to movements to be noticed later, con- 
stitutes what is commonly called respiration ; but the mere tide 
of the air inward and outward is of no significance unless the 
interchange of oxygen and carbon dioxide take place. 

Internal Respiration. — Nor is this interchange of value unless 
another occurs in the tissues. The oxygen which has entered the 
pulmonary blood is conveyed by the circulation to a point where 
the fluid is brought into very close relationship with the tissues 
(namely, in the capillaries), and is here given up to the cells ; 
furthermore, at the same place the cells give up carbon dioxide to 
the capillary blood. It is only for the purpose of effecting this 
last interchange that there is any respiration, or any respiratory 
'apparatus. Inspiration and expiration, the pulmonary inter- 
change of gases, the transportation of oxygen and carbon dioxide 

195 



I96 RESPIRATION. 

to and away from the cells, are all equally immaterial except as 
being means to the accomplishment of this end. It would make 
no difference whether pulmonary respiration were kept up or not 
if oxygen could be introduced into the blood and carbon dioxide 
removed from it in some other equally efficient way. So far as 
the cell is dependent on the acquisition of oxygen and the re- 
moval of carbon dioxide, it would make no difference if there 
were no respiration and no circulation if these materials could 
be acquired and removed in some other equally efficient way. 
On the other hand, it were useless to keep up artificial respira- 
tion or to inject oxygen into the lungs if the cells, through some 
disability, cannot take up the oxygen furnished, or if the circu- 
lation cannot absorb or convey the oxygen. 

It is seen that, from the standpoint of the blood, the inter- 
change of gases in the lungs is exactly opposite to that in the 
tissues ; that is to say, in the lungs it loses carbon dioxide and 
gains oxygen, while in the tissues it loses oxygen and gains car- 
bon dioxide. The pulmonary interchange is properly termed 
external respiration in contradistinction to that in the tissues 
which is termed internal respiration. 

It is needless to comment upon the universal necessity of oxy- 
gen to the life of cells. Its appropriation is to be looked upon 
as a part of the nutritive process \ and, indeed, while in the 
long run, cells are certainly dependent upon the nutriment fur- 
nished by the ordinary aliments, they will retain their vital ac- 
tivity for a longer time when deprived of any or all of these 
than when deprived of oxygen alone. This gas is more imme- 
diately necessary to the maintenance of life than is any other 
substance. 

Since, in order to bring about internal respiration in the 
human being, the lungs and circulation happen to be necessary, 
attention will have to be directed to the respiratory phenomena 
taking place in both. 



ANATOMY OF THE RESPIRATORY ORGANS. 



197 



Anatomy of the Respiratory Organs. 

It will be considered that the air has passed through the pos- 
terior nares into the pharynx and is ready to enter the larynx. 

The Larynx. — This lies in front of the esophagus, its upper 
opening communicating with the middle pharynx. It is composed 
of four cartilages and the muscles and ligaments which hold them 
together. The cartilages keep its lumen constantly open, while 
the muscles effect movements concerned in deglutition, respira- 

Fig. 44. 




Diagram of the Respiratory Organs. 
The windpipe leading down from the larynx is seen to branch into two large bronchi, which 
subdivide after they enter their respective lungs. (Yeo.) 

tion and phonation. The cartilages are the thyroid, cricoid and 
two arytenoids. The two alse of the thyroid meet at an acute angle 
in front to form the Adam's apple. The cricoid is at the lower 
end of the larynx, completely surrounding it. The arytenoids 
are movable and rest upon the back of the cricoid. (Fig. 45.) 
The vocal cords, two ligamentous bands covered by a thin 



I98 RESPIRATION. 

layer of mucous membrane, stretch antero-posteriorly across 
the upper end of the larynx, while the false vocal cords, hav- 
ing nothing to do with phonation, and pinker in color, are 
above and parallel with the true cords. A small triangular 
leaflet of fibro -cartilage is attached by its base to the base of the 
tongue and to the upper anterior part of the larynx. This 
is the epiglottis. It fits accurately over the opening of the 
larynx, and during the act of deglutition is closed to prevent the 
entrance of food, saliva, etc. Except during deglutition the 
epiglottis is raised and there is free passage of air into and out 
of the laryngeal cavity. The vocal cords are fixed anteriorly 
to a point between the alae of the thyroid and posteriorly to 
the movable arytenoids. Intrinsic muscles have the power of 
so moving the arytenoids as to separate and approximate the 
posterior attachments of the cords and thus increase or decrease 
the size of the rima glottidis. During inspiration these muscles 
act to separate the cords and allow free entrance of air into the 
trachea. When this act has ceased they relax and the cords are 
passively approximated. The expiratory act separates the cords 
and they afford no obstruction to the exit of air. The inspi- 
ratory act, on the other hand, tends to draw the cords together 
and the active intervention of the muscles is necessary to keep 
the glottis open. 

The Trachea. — The trachea succeeds the larynx in the respi- 
ratory tract. It begins at the cricoid cartilage and extends down- 
ward for about four and a half inches where it bifurcates to form the 
right and left bronchi, one of which goes to each lung. The trachea 
consists of an external fibrous membrane, between the layers of 
which are a number oi cartilaginoits rings, and an internal mucous 
membrane. The rings are the most striking part of the trachea. 
They serve to keep the canal open at all times. The inspiratory 
effort would otherwise collapse the walls and prevent the en- 
trance of air. These rings are sixteen to twenty in number, and 
are lacking in the posterior third or fourth of the circumference. 



TRACHEA AND BRONCHI. 



I 99 



[Fig. 45- 




Outline showing the general form of the Larynx, Trachea, and Bronchi, as 
seen from behind. 

h y great cornu of the hyoid bone; t, superior, and t' , the inferior cornu of the thyroid carti- 
lage ; e, epiglottis ; a, points to the back of both the arytenoid cartilages, which are sur- 
mounted by the cornicula ; c, the middle ridge on the back of the cricoid cartilage ; tr, the 
posterior membranous part of the trachea ; b, i/ , right and left bronchi. (Kirkes after Allen 
Thomson.} 



200 



RESPIRATION. 



They are, therefore, not true rings. The interval between their 
ends is filled with fibrous and nonstriped muscular tissue. The 
mucous membrane is lined by ciliated epithelium, and has 
mucous glands in its substance (Figs. 44, 45). 

The Bronchi. — The primitive bronchi are of the same essen- 
tial structure as the trachea. The right is the larger, shorter, 
and more nearly horizontal. This probably accounts for the 
more frequent lesions in the right lung. Penetrating the lung 
substance they divide and subdivide until each, by its ramifica- 
tions, communicates with every air vesicle in that lung. When 

Fig. 46. 



Bronc/ua! Musc/e, 



Ne/*v<?. 




Bronchi a/ /Jrtery. 



Carft/crgs 



Gfanct acfoi & c/ucf t 



T.S, intra-pulmonary bronchus of cat. PA and PV, pulmonary artery and vein ; bv, 
bronchial vein; V, air-vesicles. {Sterling.) 



the primitive bronchus has divided, the incomplete cartilagi- 
nous rings are replaced by irregular plates of cartilage, which 
are so arranged as to completely encircle the tube. These 
extend as far as the division of the tubes into branches -J-^ in. 
in diameter. 

Surrounding the tubes in the lung substance is a circular layer 



AIR VESICLES. 201 

of plain muscular fibers ; these cease only at the air vesicles. 
Elastic fibrous tissue is also present everywhere in the bronchial 
walls and is continued over the vesicles themselves. 

Bronchial tubes above -^ in. in diameter have in their walls 
cartilaginous plates, muscular tissue, fibrous elastic and inelastic 
tissue and a lining membrane of ciliated epithelium. 

Bronchial tubes -L- in. in diameter, and smaller, have in their 
walls the same elements excepting the cartilage ; but as the tubes 
subdivide their walls grow continuously thinner, and the inelas- 
tic tissue becomes less and less in amount, until it finally prac- 
tically disappears ; the ciliated epithelial cells gradually give 
place to a single layer of squamous cells in the smallest tubes. 
The smallest bronchial tubes, the bronchioles, are from y^- to 
-n^ in. in diameter. Of course everywhere in the walls there 
are vessels and nerves. 

The Air Vesicles. — Each bronchiole opens into a collection 
of air vesicles, or cells, called a pulmonary lobule. The term 
lobulette will be here applied to it, however, reserving the word 
lobule for a collection of lobulettes about \ in. in diameter. 
The bronchiole entering the lobulette becomes the infundibulinn 
(Fig. 47), a slightly dilated canal from which are given off from 
eight to sixteen oblong vesicles, the true air cells. The cells are 
a little deeper than they are wide and end in blind extremities. 
The diameter of the lobulette is about $V ~ iV * n, j tnat °^ tne 
vesicle about ^ro-yV m » It has been estimated that there are 
some 725,000,000 of these vesicles in the lungs and that their 
combined area is something over two hundred square yards. 

The walls of the air cells are very thin, being composed of a 
single layer of flattened epithelium together with highly elastic 
fibrous tissue. Ramifying in this latter is a most abundant 
supply of capillaries, which are larger here than anywhere else in 
the body. The physical conditions are most favorable for the 
exchange of gases between the blood and air, each capillary 
being exposed to vesicles on both sides, and the air and blood 



202 RESPIRATION. 

being separated only by the very thin walls of the capillary and 
vesicle. The elastic tissue is very important in expelling the 
air from the cells when the inspiratory effort has ceased. 

For the nutrition of the bronchi and lung substance arterial 
blood is furnished by the bronchial artery, which enters and 

Fig. 47. 




TERMINAL BRANCH OF A BRONCHIAL TUBE, WITH ITS INFUNDIBULA AND AIR-SACS, 

FROM THE MARGIN OF THE LUNG OF A MONKEY, 

INJECTED WITH QUICKSILVER. 

a, terminal bronchial twig; b b, air-sacs; c c, infundibula. X 10. (Kirkes after E. E. 
Schulze.) 

ramifies with the bronchi. The entire mass of venous blood 
passes directly from the heart through the pulmonary artery to 
the lungs to be arterialized, and it is the capillaries of this artery 
which furnish the abundant network between the air cells. 

The lungs have the shape of irregular cones, their bases rest- 
ing on the diaphragm and their apices extending to points a 
little above the clavicles. They are completely separated from 
each other by the mediastinum and their external surfaces are 
covered by the pleura, a serous membrane similar to the peri- 
toneum and reflected from the thoracic wall. The right lung is 
divided by fissures into three lobes and the left into two. 
Superficially the lung substance is seen to be subdivided into 
areas about \ in. in diameter called the lobules. Each lobule is 
composed of a number of lobulettes as above mentioned. 



mechanism of respiration. 203 

Mechanism of Respiration. 

Respiration implies the more or less regular entrance and exit 
of air to and from the lungs. The entrance is inspiration; 
the exit expiration. Now, the thorax is a closed cavity, not- 
withstanding the fact that the lungs have an opening (the 
trachea) by which they communicate with the external air \ and, 
so far as the simple ingress and egress of air is concerned, the 
question of pulmonary respiration resolves itself into one of pure 
mechanics. The lungs may be looked upon as a bag (or two 
bags) in the thoracic cavity. Inspired air does not enter the 
thoracic cavity, but this bag which is in it. This fact is of the 
greatest importance. 

Furthermore, the lungs are everywhere in contact with the 
thoracic wall by their pleural surfaces. They are composed very 
largely of highly developed elastic tissue, but are perfectly pas- 
sive themselves. That is to say, they possess no power of ex- 
pansion except in obedience to extraneous influences. As found 
in the thorax they possess a contractile power, but only because 
certain forces have put their elastic tissue on the stretch, and the 
contraction is a simple effort of the tissue to return to the condi- 
tion which characterized it before it was subjected to the expand- 
ing force. 

Before birth there is no air in the lungs, and this is the only 
time when the elastic tissue is not on the stretch. The bronchioles 
and air cells are collapsed, but the thorax is contracted and the 
pulmonary and thoracic walls are in contact by their respective 
pleural surfaces. When the child is born an inspiration fills the 
lungs and they are never thereafter devoid of air. They collapse 
to a certain extent and leave the thoracic wall when the chest is 
opened, but cannot empty themselves entirely because the walls 
of the bronchioles collapse before all the air can escape. This 
collapse of the lungs when the chest wall is opened shows that the 
lung structure is in a constant state of tension, which tension has 



204 RESPIRATION. 

always a tendency to empty the lungs, but cannot do so because 
the thorax can contract only so far, and when its contraction has 
reached its limit, for the lung to contract farther would mean a 
separation of the pulmonary and thoracic walls and the formation 
of a vacuum between them. The additional reason above given, 
namely, the collapse of the bronchioles before all the air can 
escape, is inoperative under normal conditions and need not be 
considered. 

Causes of Respiratory Movements. — Seeing that the lung 
structure has always a tendency to empty itself of air, it follows 
that inspiration cannot be dependent upon the lung itself. 
Granting, from the physical conditions present, that the lungs 
and thorax must expand and contract together, the expansion of 
the lungs in inspiration is a consequence and not a cause of the 
thoracic expansion, and the contraction of the lungs in expira- 
tion is a cause and not a conseque?ice of thoracic contraction. 
This statement as to expiration applies only to ordinary 'tran- 
quil respiration, as will be seen later. Speaking broadly then, 
inspiration is an active and expiration a passive process. That 
is, inspiration occurs as a result of the activity of certain muscles 
which operate to expand the thorax, and expiration as a conse- 
quence simply of the cessation of activity on the part of those 
muscles and the passive contraction of the lung tissue. 

The relation of the thorax and lungs and the action of each in 
respiration may be illustrated. Suppose a bellows, which, say 
for some mechanical reason, cannot completely collapse and 
which is itself air-tight, to contain a thin rubber bag communi- 
cating by a tube with the external air ; suppose the bag con- 
forms in general outline to the shape of the bellows, and under 
a moderate degree of distention completely fills the cavity of the 
bellows when the latter is collapsed as far as possible. Now, it 
being understood that the bag was somewhat distended to cause 
it to fill the bellows, and that all air has been allowed to escape 
by a temporary opening from between the walls of the two and 



RESPIRATORY MOVEMENTS. 205 

the bellows itself made air-tight afterward, it follows that unless 
the bellows can contract the bag will remain distended and will 
not leave the bellows wall, although it will have a constant ten- 
dency to do so. It is also apparent that, since the bag exerts a 
continual compressing effect on its contents, the pressure inside 
it will be greater than that outside between it and the bellows 
wall. Under these conditions there will be a constant tendency 
on the part of the bellows to collapse, and some active force will 
be necessary to expand it ; when it is made to expand the con- 
tained bag will expand with it. Suppose the expansion to be 
stopped at a certain point and the bellows held (to prevent con- 
traction) ; it is obvious that now the pressure inside the bag is 
greater, while that outside between its walls and those of the bel- 
lows is less, than when the expansion began ; that is, the bag has 
become distended more and is exerting a greater compressing 
effect upon its contents. If now the bellows be simply released, 
both the bag and the bellows will contract and the former will 
empty itself so far as the latter will allow, but when the bellows 
has reached the limit of its contraction the bag also ceases to 
contract, although it remains in a constant state of tension. If 
at any time air be admitted to the bellows proper the bag will at 
once collapse. 

This illustration can be applied to the mechanical principles 
obtaining in ordinary respiration. The bellows is the air-tight 
thorax which cannot contract beyond a certain point ; ■ the 
rubber bag is the elastic lungs under constant tension, communi- 
cating by the trachea with the external air and following, or 
being followed by, the movements of the thorax ; the pressure 
in the bag and between it and the bellows wall represents the 
intrapulmonary and intrathoracic pressures respectively. 

It will be noticed later that this illustration does not go quite 
far enough to explain a few of the phenomena of expiration, but 
it could very easily be made to do so. 

Inspiration. — Any force which expands the thorax aids in in- 



206 RESPIRATION. 

spiration • and any muscles which increase any of the thoracic 
diameters expand the thorax. The diameters increased are chiefly 
the (i) vertical and (2) anteroposterior. 

The vertical is increased by descent of the diaphragm, which 
descent is caused by its contraction, since, owing to the intra- 
thoracic i l pull ' ' exerted upon it, it is normally vaulted upward. 

The antero-posterior diameter is increased chiefly by the eleva- 
tion of the ribs. Since these bones, attached posteriorly to the 
spinal column, run not only forward but also downward to join 
the sternum by the costal cartilages, it follows that the elevation 
of their anterior ends will increase the diameter in question. 

Muscles of Inspiration. — Elevation of the ribs is effected by a 
number of muscles. The three scaleni are attached above to the 
cervical vertebrae and below to the first and second ribs ; their 
action elevates not only these ribs but the whole anterior chest 
wall. 

The action of the intercostales externi is still a subject of dis- 
pute in connection with the physiology of respiration. These 
muscles are attached externally to the adjacent borders of the ribs, 
and thus occupy the intercostal spaces. Their fibers are directed 
downward and forward, and the effect of contraction of any single 
intercostal muscle would be to approximate the two ribs to which 
it is attached; but if it can be assumed that the first rib is fixed, 
then, from the direction of their fibers, the external intercostals 
will render the ribs more nearly horizontal by raising their an- 
terior movable extremities. It seems that the first rib is pre- 
vented from descending, probably by the simultaneous contraction 
of the scaleni. The i7itercostales intei'ni have a direction almost 
at right angles to that of the externi ; the sternal portions of 
these act from the sternum and also elevate the anterior extremi- 
ties of the ribs. The levatores costarum are attached to the 
transverse processes of the dorsal vertebrae and to the upper borders 
of the ribs posteriorly. The transverse processes are fixed points 
and the ribs are movable on their spinal articulations. Contrac- 



INSPIRATION AND EXPIRATION. 207 

tion of these muscles is, therefore, very efficient in elevating the 
anterior ends of the ribs. 

The action of the diaphragm is the most notable of the mus- 
cular phenomena connected with respiration, and it deserves to 
be called the 6 ' muscle of respiration. ' ' 

These are the muscles which are chiefly concerned in ordi- 
nary inspiration. Their combined action also increases slightly 
the transverse diameter of the chest. But there are certain 
others, known as auxiliary muscles of inspiration, which are called 
into play during profound or forced inspiration. Their action 
is evident from their attachments — all operating chiefly to in- 
crease the antero -posterior diameter. They are the serratus 
posticus superior, sterno-mastoideus, levator anguli scapulce, tra- 
pezius, pectoralis minor, pectoralis major (costal portion) , serratus 
magnus, rhomboidei and erectores spince. It will be noticed that 
several of these which usually take their fixed points on the 
chest, as for example, the sterno-mastoideus, pectorales, etc., 
must, in order to aid inspiration, take their fixed points at their 
other extremities. 

Expiration. — When the force which expands the chest during 
inspiration ceases to operate, expiration follows. Not only does 
the elastic (i) lung tissue force out the air, but the (2) thoracic 
walls, by their costal cartilages and their intercostal tissues, 
are themselves elastic, and this elasticity, aided by the (3) 
"tone" of the muscles which have been put upon the stretch 
during inspiration and which are now seeking to return to their 
normal condition, tends to restore the thorax to the dimensions 
it had previous to the inspiratory act. So far no actual muscu- 
lar contraction has been brought into play, and it is here as- 
sumed that none is usually concerned in the expiratory act of 
ordinary tranquil respiration. 

Some maintain that the costal portions of the intercostales 
inter ni particularly are expiratory in quiet breathing ; they do 
contract and the ribs approach each other during the act, but it 



208 RESPIRATION. 

is probable that they serve only to maintain the proper degree 
of tension of the intercostal tissues. 

Although the elastic reaction of the lung tissue during expira- 
tion operates together with the elasticity of the thoracic wall in 
diminishing the antero-posterior diameter of the chest, it is 
chiefly effective in diminishing the vertical diameter by raising 
the diaphragm. It exerts a certain " suction " upon that muscle 
causing it to arch upward in following the contracting lungs. 
It is seen, therefore, that during inspiration the chest wall and 
diaphragm exert " suction " upon the lungs, causing them to fol- 
low, and during expiration the lungs exert "suction " upon the 
chest wall and diaphragm, causing them to follow. 

Forced Expiration. — It is evident that, while ordinary expi- 
ration is a passive process, a person can voluntarily force out of- 
his lungs more air than is ordinarily expelled, as in singing, 
blowing, talking, etc. This is effected by certain muscles 
whose contraction diminishes the thoracic capacity, chiefly by 
depressing the ribs and elevating the diaphragm. Those which 
depress the ribs are the intercostales interni, infracostales and 
triangularis sterni. Those which elevate the diaphragm do so 
by compressing the abdominal contents and forcing them up 
against that muscle. They are the obliquus externus, obliquus 
internus transversalis and rectus abdominis. These depress the 
chest wall as well. 

Rhythm of Respiration. — Under ordinary conditions inspira- 
tion and expiration follow each other in a regular rhythmical 
fashion. Some hold that an interval follows inspiration before 
expiration begins, but this is probably not correct. Indeed, it 
is doubtful if there be an interval following expiration, though 
it will be here considered that there is a brief one. Expiration 
is a little longer than inspiration. The inspiratory act is of uni- 
form intensity throughout, while the expiratory act gradually 
diminishes in intensity as it approaches completion — a circum- 
stance to be expected from the physical conditions causing it. 



RESPIRATORY SOUNDS. 2CXQ 

After every six to ten respiratory acts a more profound (sigh- 
ing) inspiration than usual is taken, the effect being a more 
thorough changing of the pulmonary contents. Coughing, 
sneezing, hiccoughing, laughing, etc., all interfere with rhyth- 
mical respiration. 

Modified Respiration. — In coughing and sneezing a profound 
inspiration precedes a violent convulsive contraction of the ex- 
piratory muscles. Sighing is an expression on the part of the 
tissues that more oxygen is needed and that, therefore, the con- 
tents of the lungs must be more completely changed. Yawning 
is a phenomenon similar to sighing, but may not represent de- 
ficient oxygenation, as when it occurs from contagion. Except 
in the contraction of different facial muscles, sobbing and laughing 
are identical from a respiratory standpoint ; in both there is a 
succession of quick contractions of the diaphragm. Hiccough is 
an involuntary contraction of the diaphragm accompanied by 
closure of the glottis. It takes place during inspiration. In 
hawking the glottis is open and a continuous expiratory current 
is sent through the narrowed passage between the base of the 
tongue and the soft palate. Snoring occurs with the mouth 
open • the current of air throws the uvula into vibration and 
produces the characteristic sounds. 

Sounds of Respiration. — When the ear is applied to the 
chest there is heard during inspiration a breezy expansive sound 
of slightly increasing intensity throughout, and ceasing abruptly 
at the end of the act. Immediately begins the expiratory sound, 
very short, lower in pitch than the inspiratory, and gradually 
decreasing in intensity until it is lost before expiration is more 
than one-fourth finished. When listening over a large bronchus 
this sound is prolonged and has a higher pitch than usual. 
Respiratory sounds are more pronounced in the female than in 
the male chest, owing to the predominance of costal breathing in 
the former sex. 

Rate of Respiration. — The respiratory rate sustains a fairly 

14 



2IO RESPIRATION. 

constant relation to the cardiac rate, the ratio being about one 
to four. This makes the average number of respirations about 
eighteen per minute for adults. In a general way this rate is sub- 
ject to variations from the same causes as that of the pulse. Any 
appreciable fall in the amount of oxygen in the inspired air will 
increase the number of respirations for obvious reasons. The 
frequency and depth usually bear an inverse ratio to each other. 
Types of Respiration. — (i) Costal respiration is that carried 
on by the chest walls ; (2) diaphragmatic, that effected by the 
diaphragm. In the former type movements of the thorax are 
concerned ; in the latter, movements of the abdomen. Accord- 
ing as the movements in costal respiration are more pronounced 
in the upper or lower segment of the chest, that type is subdi- 
vided into (<?) superior costal and (F) inferior costal. 

In young children the diaphragmatic, or abdominal, type pre- 
vails ; in adult males a combination of the inferior costal and 
abdominal ; in adult females the superior costal. The last cir- 
cumstance is probably due in part to the mode of dress in civil- 
ized countries, and in part to the provision against encroachment 
of the uterus upon the abdominal cavity during pregnancy. 

Intrapulmonary and Intrathoracic Pressure. — It is evident 
that during inspiration the pressure inside the lungs (intrapul- 
monary) is less than the ordinary atmospheric pressure ; this, 
in fact, is the immediate cause of the entrance of air. It is 
also evident that during expiration the intrapulmonary pressure, 
owing to the compressing effect of the lung tissue and the tho- 
racic walls, is greater than the outside atmospheric pressure ; 
this is the immediate cause of the exit of air. In both acts the 
air rushes in or out, as the case may be, in an effort to maintain 
the same pressure inside the lungs as exists in the surrounding 
atmosphere. It is convenient to call the pressure which is less 
than atmospheric negative, and that which is greater positive 
pressure. 

The intrapulmonary pressure is negative during inspiration and 



PULMONARY CAPACITY. 211 

positive during expiration. Now, owing to conditions already 
referred to, as the chest and lungs expand during inspiration, the 
pressure between the adjacent walls of the two (intrathoracic) 
becomes less and less and reaches a minimum at the end of that 
act. Furthermore, owing to the continuous "pull" of the 
elastic lungs upon the chest walls the intrathoracic pressure re- 
mains negative even at the end of expiration. But it can be 
made to become positive under forced action of the expira- 
tory muscles, as in coughing, blowing, etc. The constantly 
increasing negative condition of intrathoracic pressure is evi- 
denced by a drawing in of the intercostal tissues during inspira- 
tion ; when the pressure assumes a positive character, as in the 
expiratory acts of the pulmonary emphysema, these tissues bulge 
outward. 

Pulmonary Capacity. — It is evident that the most forcible 
expiration cannot completely empty the lungs of air. The air 
remaining after such an effort is the residual air. It amounts 
to about ioo cubic inches. But in ordinary respiration at the 
end of the expiratory act there is more than ioo cubic inches 
of air in the lungs, because in such cases all the air possible is 
not forced out. In fact about 200 cubic inches usually remain ■ 
this consists of the residual plus another 100 cubic inches, which 
is called the reserve or supplemental air. It can be forced out, 
but is not in tranquil respiration. The amount of air which is 
taken into the lungs by an ordinary respiratory act amounts to 
about 20 cubic inches, and is termed tidal air. It is the only 
volume used in quiet breathing. At the end of the inspiratory 
act in tranquil respiration it is obvious that the expansion may 
continue still farther, and a certain amount of air, over and 
above the tidal air, be taken into the lungs. The maximum 
amount which can be so inspired (beyond the tidal) is about 
no cubic inches, and is the complemental air. 

It is seen, then, that the entire lung capacity is equal to about 
330 cubic inches. But the residual air cannot under any cir- 



212 RESPIRATION. 

cumstances be called into use, and consequently the vital capac- 
ity is equal to the total capacity minus the residual air (100 
cubic inches), or 2jo cubic inches. It is the volume which can 
be expelled by the most forcible expiration after the most for- 
cible inspiration. 

The capacity of the trachea and larger bronchi is known as 
the bronchial capacity, and amounts to about 8 cubic inches. 

The quantity of air in the small bronchioles and air vesicles 
is increased by inspiration and decreased by expiration ; it is 
called alveolar capacity, and at the end of ordinary expiration 
amounts to about 150 cubic inches. Quiet inspiration increases 
it to about 180 cubic inches. 

All these estimates, of course, represent only an average. 
The vital capacity is increased by stature, by any occupation 
which calls for active physical work and by various other con- 
ditions. 

Composition of Air. — Ordinary atmospheric air contains, in 
round numbers, about 21 parts of oxygen to 79 parts of nitro- 
gen. These two gases make up the main bulk of the atmos- 
phere. In addition, the atmosphere always contains a little 
carbon dioxide (about .04 per cent.), ammonia, moisture, or- 
ganic material, dust, nitric acid, etc. All except the oxygen 
and nitrogen are of minor importance in respiration when they 
are not present in amounts beyond the usual. It will be seen 
that the striking difference between inspired and expired air is 
in the proportions of oxygen and carbon dioxide. 

Diffusion in the Lungs. — The expired air contains much more 
C0 2 and much less O than the inspired air. The interchange 
of gases between the alveolar air and the blood is responsible for 
the difference. 

The question is what forces cause the O of the air to enter the 
alveoli and the C0 2 to leave it. As might be supposed, the air 
escaping during the first part of expiration differs very little in 
composition from the inspired air, for it has been occupying the 



DIFFUSION IN THE LUNGS. 213 

upper air passages where no interchange occurs. The bronchial 
capacity is only about one-third large enough to accommodate the 
tidal air, and consequently the greater part of it must come from 
lower down in the lung structure, and the C0 2 in the expired air 
continuously increases until the end of the act. At each inspira- 
tion at least two thirds of the tidal air must pass into the small 
bronchi, or lower. Thus it is that inspiration and expiration 
themselves, taking into and bringing out of the vesicles (or at 
least the bronchioles) air fresh with O and air vitiated with 
C0 2 , aid very materially in keeping constant the composition 
of the alveolar air. 

In the second place, the cardiac movements have a similar ef- 
fect, each systole decreasing the size of the heart and inducing a 
fresh atmospheric current toward the deep alveoli, and each dias- 
tole forcing a like current of vitiated air toward the trachea. 
This force is not inconsequential. 

In the third place, the diffusibility of gases under known phys- 
ical laws, without the aid of any such movements as have been 
described, is an occurrence in connection with the phenomenon 
in question. Every gas, under ordinary atmospheric conditions, 
exerts a certain pressure. In every mechanical mixture of gases 
(such as the atmosphere) each individual gas exerts a part of 
the total pressure — a part proportional to its percentage in that 
mixture. This has been called the "partial pressure " of that 
gas. Since O is present in ordinary atmosphere to the extent of 
21 parts per hundred, the partial pressure of oxygen in the 
atmosphere is -f^ of the total pressure. 

Now, in the air of the alveoli O is present to a less extent than 
2 1 parts per hundred, and consequently its partial pressure in 
that situation is less than in the trachea and bronchi. The re- 
sult is that O continually makes its way from the point of higher 
pressure (trachea and bronchi) toward the point of lower pres- 
sure (alveoli). The tendency is thus to establish a uniform 
partial pressure throughout the whole respiratory tract ; but 



2 14 ' RESPIRATION. 

this is never done during life because the partial pressure above 
is being continually increased by the introduction of new O, 
and below is being continually diminished by the removal of 
that gas from the alveoli by the blood. 

In case of C0 2 opposite conditions prevail. This gas is being 
continually introduced into the alveolar air from the blood, and 
consequently it is present there in much larger quantities than 
in the trachea and bronchi, which contain newly inspired air. 
The partial pressure, therefore, of C0 2 in the alveoli is much 
higher than in the upper respiratory passages, and a continual 
current of it diffuses upward to equalize the pressure ; this is 
never accomplished, however, for reasons of similar nature to 
those keeping up the constantly unequal pressure of O. 

These three factors — respiratory and cardiac movements and 
the natural diffusion of gases — are, therefore, in continual opera- 
tion to get O to and C0 2 away from the alveoli. Under their in- 
fluence the composition of the alveolar air remains fairly uniform. 

Alterations of Air in the Lungs. — These are chiefly : (a) Loss 
of oxygen, (/;) gain of carbon dioxide, (V) elevation of temper- 
ature, (V) gain of water, (<?) gain of ammonia, (/) gain of 
organic matter, (g) gain of nitrogen, (//) loss of (actual) vol- 
ume. The capital changes are loss of O and gain of C0 2 . 

(a) Loss of Oxygen. — The air in passing through the lungs 
loses of O nearly 5 per cent, of its total volume. That is, whereas 
on entering it contains 2 1 parts, on leaving it contains only about 
16 parts per hundred of this gas. Nearly 25 per cent, of the 
total volume of O inspired, therefore, is lost in the lungs. 

When the respirations are 18 to the minute, and 20 cu. in. of 
air are inspired at each breath, the amount inspired in an hour will 
be 21,600 cu. in. Since a little more than one-fifth of this air 
is O, and since only one-fourth of the inspired O is consumed, 
the total amount necessary for an hour will be about 1,100 cu. in. 
This allows, however, for no muscular, digestive or other activ- 
ity, and the amount actually necessary is larger than this. 



CHANGES OF AIR IN THE LUNGS. 



2I 5 



The circumstances which call for an increase in almost in- 
variably cause an increase in the output of C0 2 . 

(/;) Gain of Carbon Dioxide. — The amount of C0 2 in inspired 
air is about .04 part per hundred (4/100 per cent.); the amount 
in expired air is something more than 4 parts per hundred. In 
round numbers then, the air in passing through the lungs gains of 
C0 2 4 per cent, of its entire volume. This is in periods of rest 
from exercise, digestion, etc. The total amount discharged in 
one hour is, on an average, about 1,000 cu. in. This estimate 
should probably be raised to 1,200 cu. in. for ordinary activity, 
and varies according to many conditions, some of which are 
rapidity and depth of respiration, age, sex, digestion, diet, sleep, 
exercise, moisture, temperature, season, integrity of the nerve 
supply, etc. 

The subjoined table from Kirkes' Physiology compares the 
composition of inspired and expired air. 



Inspired Air. 



Expired Air. 



Oxygen . . 
Nitrogen . 
Carbonic acid . 
Watery vapor. . 
Temperature 



20.96 vols, per cent. 
79 

0.04 " " 

variable. 



16.03 vols, per cent. 
79 ' « 
4.4 " 

saturated, 
that of body (36 C.] 



Conditions Influencing Output of CO r — When the rapidity of 
respiration is increased, the depth remaining constant, the per- 
centage of C0 2 in the expired air is reduced because more air is 
respired, but the total quantity in any given time is increased. 
The same result follows an increased depth and a constant rate. 
With a diminished rapidity and increased depth more C0 2 is 
exhaled than under opposite conditions. 

The amount of C0 2 exhaled is small in very young infants. 
But soon the qutput begins to increase, and in males continues to 
do so up to about thirty years ; there is then a slight decrease up 
to sixty, and afterward a considerable decrease to death. 



2l6 RESPIRATION. 

In the female the output is less than in the male. In the former 
sex the increase is said to cease at puberty and to remain con- 
stant until the menopause, after which time it increases to sixty 
and diminishes subsequently. 

During digestion the quantity is considerably increased. This 
is probably due to the muscular activity of the alimentary tract, 
to glandular metabolism and to changes taking place in the food 
products. 

As to diet, it may be said in general that the exhaled C0 2 is 
increased in quantity by the taking of nitrogenized foods, tea 
and coffee. 

The influence of sleep is to diminish the output. 

Muscular exercise is very efficient in increasing the amount of 
C0 2 exhaled ; in fact, this explains- partly the variations in con- 
nection with sex, digestion, sleep, etc. 

A high degree of moisture increases the exhalation, as does 
a rise in body temperature. A rise in external temperature, how- 
ever, has an opposite effect. 

The output is increased in spring and decreased in autmnn. 

When the efferent nerve supplying a part is severed the pro- 
duction of C0 2 in that part is at once diminished. 

The consumption of O and the exhalation of C0 2 bear a fairly 
constant relation to each other — any condition increasing one in- 
creasing the other, and vice versa. The facts, therefore, which 
have been mentioned as governing the exhalation of C0 2 may 
be applied to the consumption of O. 

(V) Gain in Temperature. — When the body temperature is 
normal and the external atmospheric temperature about 70 F., 
it is found that air inspired through the nose and expired through 
the mouth has its temperature raised from 70 ° to about 95 °; 
the rise is less when inspiration takes place through the mouth. 
The last air of expiration is warmer than the first. This gain 
of heat while the air is in the lungs needs no explanation when 
it is remembered that the average temperature of the tissues 
with which it is in contact is 98. 5 ° F., or higher. 



AMOUNTS OF O CONSUMED AND C0 2 EXHALED. 217 

(a 7 ) Gain of Water. — This water is in the form of vapor. 
It is natural that the air should absorb water from the moist sur- 
faces with which it is in contact. The capillary network with 
which it is in close relation supplies moisture to the mucous 
membrane not only of the alveoli but of the entire respiratory 
tract. One or two pounds of water are eliminated thus daily. ■ 

(V) Gain of Ammonia. — Ammonia is exhaled in small quan- 
tity by the lungs. It is insignificant except in cases of sup- 
pressed kidney action. 

(/) Gain of Organic Matter. — The quantity of organic mat- 
ter exhaled by the lungs is inconsequential (unless ventilation 
be bad), but such exhalation does occur to a small extent. It 
gives the odor to the breath. 

(g) Gain of Nitrogen. — The exhalation of this gas by the 
lungs is of no respiratory importance. The amount is said to 
be y-g-o^o" tne amount of oxygen consumed. An occasional 
loss of nitrogen has been observed. 

(Ji) Decrease of (Actual) Volume. — When the external tem- 
perature is below about 90 ° F. the volume of expired air is a 
little greater than that of the inspired air, because of the in- 
crease of temperature it undergoes in passing through the lungs. 
But the actual volume of the expired air, when reduced to the 
same temperature as the inspired, is found to be always a little 
less than that of the latter. It is estimated that from 7 1 -- & 1 1) of 
the total volume of the inspired air is thus lost in respiration. 

Besides the substances mentioned as being exhaled from the 
lungs, it is well known that odorous emanations proceed from 
them after garlic, onions, turpentine, alcohol, certain drugs, 
etc., have been taken into the stomach. 

Relation Between Oxygen Consumed and Carbon Dioxide 
Exhaled. — A given volume of O will combine with carbon to 
form the same volume of C0 2 ; or the amount of O in a given 
volume of C0 2 is equivalent to that volume when set free from 
the carbon. A cubic foot of O will unite with carbon to form 



2l8 RESPIRATION. 

a cubic foot of C0 2 ; or a cubic foot of C0 2 will yield, on dis- 
sociation, a cubic foot of O. 

This being the case, if all the O consumed in the lungs were 
exhaled therefrom in the form of C0 2 , the amount of C0 2 ex- 
haled would just equal the amount of O consumed. But the 
amount of consumed O is about 5 per cent, of the inspired air, 
while the amount of exhaled C0 2 is only about 4 per cent, of 
the expired air. It follows, therefore, that 1 per cent, of the 
volume of inspired air is not represented by the C0 2 exhaled 
from the lungs and skin. The relation between the consumed O 
and the exhaled C0 2 is usually expressed as the " respiratory quo- 
tient " — the division of the latter by the former giving the quo- 
tient. This quotient is made to vary by many circumstances, 
though for any considerable period its average is about the same. 

While it has been stated that the O absorbed and the C0 2 pro- 
duced vary together usually, they are in a certain measure inde- 
pendent of each other. For C0 2 does not result from the im- 
mediate union of O with carbon of the carbohydrates and fats, 
but may be stored in the shape of complex compounds, which 
may later split up with the formation of C0 2 , either by oxida- 
tion or by intra-molecular cleavage. Furthermore, more O is 
necessary to oxidize (that is, to form carbon dioxide) some 
molecules than others. A fat requires considerably more O to 
produce C0 2 than does a carbohydrate ; so that the kind of 
food in store would also affect the respiratory quotient. 

With respect to the O which, in the long run, is not repre- 
sented in the C0 2 exhaled from the lungs and skin, it is certain 
that when various of the proximate principles are broken down 
at least a part of it is appropriated by hydrogen to form water. 

Source of Exhaled Carbon Dioxide. — The increase of C0 2 in 
expired air over the small amount contained in inspired air is 
derived from the venous blood circulating through the lungs. It 
exists in that blood under a constant tension, as is demonstrated 
by its escape when the blood is placed in a vacuum. The total 



CONDITION OF CO, IN THE BLOOD. 219 

amount escapes when the blood intact is placed in vacuo : when 
the corpuscles alone are so treated they yield up all their C0 2 , 
though it is small in amount ; but the plasma alone in vacuo yields 
a less amount than when it contains corpuscles. If, now, corpus- 
cles be added to the plasma the total amount of C0 2 is forthcom- 
ing. The corpuscles must, therefore, act as an acid causing the 
liberation of this gas from the plasma. It is probably the 
hemoglobin, or oxyhemoglobin, which has this effect, though in 
the laboratory the phosphates and certain proteids of the corpus- 
cles produce a like reaction when brought in contact with the 
carbonates and bicarbonates of soda. 

Condition of C0 2 in the Blood. — About 5 per cent, of the total 
amount of C0 2 in venous blood is in simple solution in the 
plasma; about 75-85 percent, is in loose chemical combination 
in both corpuscles and plasma; the remaining 10-20 per cent, 
is in comparatively stable combination in the plasma. Of the 
75—85 per cent., by far the largest part is in the plasma, prob- 
ably in a condition of loose association with sodium to form 
carbonates and bicarbonates ; the small part in the corpuscles 
may exist in a similar state, but it is now thought to exist in 
combination with the proteid portion of hemoglobin. The 
total 75-85 per cent, in corpuscles and plasma is so loosely com- 
bined that the mere diminution in pressure in the lungs is prob- 
ably sufficient to liberate it. The 10-20 per cent, in firm 
chemical combination is that part which cannot be extracted 
from plasma alone in vacuo, but which is dissociated on the ad- 
dition of an acid, or corpuscles, or hemoglobin, etc. It may 
be that as the blood passes through the lungs there is set free, 
iii the formation of oxyhemoglobin, an acid which immediately 
unites with the bases holding the C0 2 in combination — the lib- 
eration of the latter being the consequence. 

The O being thus in the air vesicles, and the C0 2 thus free, or 
set free, in the blood, with the very thin animal membrane con- 
sisting of the vesicular and capillary walls between them, it re- 



2 20 RESPIRATION. 

mains to be seen what forces are concerned in the interchange 
of these gases. It has been noted that only one-fourth of the O 
entering the lungs in the air is taken up by the blood ; so it is to 
be remembered that not all the C0 2 entering the lungs in the 
venous blood is taken up by the air. 

Interchange of Oxygen and Carbon Dioxide in the Lungs. — 
The condition of ' i partial pressure ' ' of gases in mixtures has 
been mentioned. Each gas exerts a pressure in proportion to 
its percentage in the mixture, and this is called its " partial 
pressure." Now, the extraction of O and C0 2 from the blood 
by placing it in a vacuum shows that both these gases exist in 
the blood under a certain degree of tension. 

The tension of a gas in solution being only the pressure nec- 
essary to keep it in solution, it follows that if the pressure be 
diminished the gas will partly escape. If an atmosphere con- 
taining, say, O at a certain partial pressure be brought in con- 
tact with a fluid containing O at a certain tension, unless the 
partial pressure of the O in the air be equal to its tension in 
the fluid there will be an escape of the gas from the point of 
higher to the point of lower pressure or tension. If the partial 
pressure of the gas be less in the atmosphere than its tension in 
the fluid, the current will be from the latter to the former and 
vice versa. This will be the case whether the media are in 
actual contact or separated by an animal membrane. 

This is the condition which obtains in the pulmonary alveoli. 
The partial pressure of O in the alveolar air is much greater 
than the tension of O in the blood ; consequently the current is 
from the air to the blood. The tension of C0 2 in the venous 
blood is much greater than the partial pressure of the C0 2 in the 
alveolar air • consequently the current is from the blood to the 
air. 

But, here, as in the last analysis of almost all physiological 
phenomena, it is found that, while these purely physical laws 
are certainly concerned in the pulmonary interchange of gases, 



ALTERATIONS OF BLOOD IN THE LUNGS. 2 2 1 

they are insufficient to explain the occurrences in full. For the 
blood will take from the alveolar air more than enough O to 
establish an equilibrium of tension and partial pressure ; the ten- 
sion of O in arterial blood is higher than its partial pressure in 
alveolar air. So it is found that the alveolar air will remove more 
than enough C0 2 to establish a similar equilibrium of this gas. 
It is known that the avidity (chemical) of corpuscles for O to 
form oxyhemoglobin causes the blood to appropriate more O 
than it would otherwise do, but even then we are driven to the 
usual ultimatum of ascribing some peculiar office to the living 
epithelium of the intervening membrane. 

Condition of Oxygen in the Blood. — Almost all the oxygen 
is conveyed in the blood by the red corpuscles, where it exists 
in rather unstable composition with hemoglobin (probably with 
its pigment portion) under the name of oxyhemoglobin. Only a 
comparatively small part is held in solution by the plasma. 
Dissociation of oxyhemoglobin occurs when the pressure is suf- 
ficiently reduced. 

Alterations in Blood in Passing Through the Lungs. — The 
sum total of the changes taking place in the blood as it passes 
through the lungs is represented by the term arterialization. In 
general, it may be said that the blood undergoes changes exactly 
opposite to those of the air in circulating through the pulmonary 
structure, and reference to the list of substances gained and lost 
by the air will suggest the main alterations in the blood. 

Of course the most striking phenomena are the loss of C0 2 
and the gain of O. In ioo volumes of arterial or venous 
blood there are found to be, on an average, 60 volumes of O 
and C0 2 . This total remains approximately constant, though 
the relative amount of each gas varies according as the blood is 
venous or arterial, and in venous blood under the influence of 
several conditions to be mentioned. In arterial blood the O 
will represent about 20, and the C0 2 about 40, of the total 60 
volumes per hundred of gas. In ordinary venous blood the O 



22 2 RESPIRATION. 

will represent about 7 volumes less (13), and the C0 2 about 7 
volumes more (47), of the total 60. In both venous and arte- 
rial blood there is an insignificant amount of nitrogen, which is 
usually present to the extent of 1.5 volumes per hundred. 

The proportion of gases is about the same in arterial blood 
taken from any part of the system. In blood coming from ac- 
tively secreting glands the ratio of O to C0 2 is nearly the same 
as in arterial blood ; in fact, such blood may have a red (arterial) 
instead of a blue (venous) color. This is because during ac- 
tivity blood is sent to the gland in increased amount to furnish 
materials for secretion, while the demand for oxygen is not rel- 
atively increased in that gland. 

Besides the changes which are apparent on referring to the 
alterations in the air in passing through the lungs, there are cer- 
tain other general characteristics which distinguish arterial from 
venous blood. The most noticeable is color. Venous blood is 
changed in the lesser circulation from a dark blue, or black, to 
a bright red. This is due to the formation of oxyhemoglobin. 
The change of color does not occur when the appropriation of 
O is interfered with, as when air is excluded from the lungs, 
or when carbon monoxide is inhaled. Again, there is every 
reason to believe that venous blood coming from different organs 
differs in composition according to the special materials which 
have been extracted from it by those organs ; the portal blood 
during digestion must certainly be different in composition from 
the general venous blood, and so it may be conceived that the 
blood coming from no two different sets of capillaries is identi- 
cal. When all this meets in the right side of the heart and is 
sent thence into the lungs it has a nearly uniform composition, 
and needs only to receive O before it can supply the wants of 
any particular tissue in the body. Arterial blood is also more 
coagulable than venous. 

Internal Respiration. — It has been said that the object of 
external respiration and the transportation of O and C0 2 is to 



INTERNAL RESPIRATION. 223 

make internal respiration possible. Oxygen, leaving the alveoli 
in a manner already described, enters the blood and at once 
combines with hemoglobin of the red corpuscles to form oxy- 
hemoglobin, A small portion of the O is used 2tp by the cor- 
puscles in transit, with the production of CO, and other meta- 
bolic materials — the corpuscles requiring O in their metabolism 
just as do other cells. But by far the largest portion is carried 
to the capillaries, where it is taken up by the cells. At the same 
time the cells give up to the blood CO, — a result of their meta- 
bolic activity. The blood, having thus given up its O, is changed 
in color, and carries the CO, back to the lungs to be exhaled. 

To furnish O and to remove CO, is the only object of respira- 
tion. Living tissue exposed to an atmosphere containing O will 
consume O and exhale CO, even if no blood be circulating 
through it. The exact manner in which a cell uses O is not 
apparent. It is evidently an oxidation process which produces 
C0 2 , and O is directly necessary to this process. But the 
amount of CO, produced in any given time may not correspond 
to the amount of O consumed in that time ; it may be greater 
or less. " It is probable that during rest O is utilized to some 
extent in oxidations which are not at once carried to their final 
stage and in which relatively little CO, is formed ; hence during 
activity comparatively little O is required to cause a final disin- 
tegration of the now partially broken down substances, and 
thus to give rise to a relatively large formation of C0 2 ' ' 
(Reichert). 

The absorption of O is to be looked upon as a part of the 
nutritive process just as the absorption of proteid, e. g., and CO, 
as one of the products of destructive metabolism just as urea. 
There is small probability that the O unites directly with the 
carbon of any of the proximate principles — although this is the 
final result. 

Interchange of Oxygen and Carbon Dioxide in the Tis- 
sues. — Here application of the principles governing the inter- 



2 24 RESPIRATION. 

change of these gases in the lungs applies. It is found that 
the tissues act as very strong reducing agents upon oxyhemo- 
globin, setting free the O. Now the tension of O in the arterial 
capillaries is much higher than in the tissues \ in fact, it is prac- 
tically nothing in the latter situation, for the O enters so quickly 
into combination that there is very little to be found here at any 
time. Consequently physical laws encourage the passage of 
this gas out of the capillaries into the tissue. 

On the other hand, the tension of C0 2 in the tissues is much 
higher than in the blood, and the same physical laws encourage 
a current of C0 2 toward the blood. Nevertheless, these laws do 
not explain all the phenomena of interchange ; the activity of 
the cells is an important agent, though their influence may be 
of a chemical nature only. 

Cutaneous Respiration. — Cutaneous respiration in man is in- 
significant and not essential to life. The skin absorbs a little O 
and exhales a little more C0 2 . It is estimated by Scharling that 
the skm performs about -^ of the respiratory function. Death 
following the covering of the body surface with an impermeable 
coating is not due to interference with cutaneous respiration. 

Ventilation. — Persons breathing in a confined space gradually 
consume the O and increase the C0 2 of the atmosphere. When 
the amount of O has been decreased to fifteen parts per hundred 
it is insufficient for the respiratory demands. When the C0 2 is 
increased to .07 part per hundred the air becomes disagree- 
able and close * this is not, however, from the accumulation of 
C0 2 so much as from organic emanations and disagreeable odors 
from the body, clothing, etc. It is only that the amount of C0 2 
serves as an indication of the extent of accumulation of these 
materials that the amount . 07 % is fixed as the limit beyond which 
it ought not to be present. This percentage of C0 2 in air free 
from emanations, etc., is not deleterious. 

Since 1,200 cu. in. of O are consumed per hour, about 15 cu. 
ft. will be necessary for a day ; and since the 1,200 cu. in. con- 



ABNORMAL RESPIRATION. 225 

sumed represent only about one- fourth of the O inspired, 60 
cu. ft. will be necessary for inspiration during twenty-four hours. 
This amount represents some joo cu. ft. of atmospheric air — 
which an ordinary person must have in that time. 

But this estimate allows nothing for increased respiratory ac- 
tivity, which inevitably occurs from some of the numerous con- 
ditions influencing it. It is found that in prisons and other in- 
stitutions of confinement it is not safe to allow each person less 
than 1,000 cu. ft. of atmospheric air. In crowded houses, where 
this space per individual cannot be obtained, it is necessary, in 
order to avoid unpleasant results, to change the air continuously, 
or at frequent intervals. Natural and artificial means are em- 
ployed to accomplish this end. 

Respiration of Various Gases. — The inhalation of pure oxygen 
is not deleterious unless it be under higher tension than in atmos- 
pheric air, when it becomes a local irritant. The blood will 
not, however, appropriate more than the usual amount. 
Nitrous oxide will sustain respiration for a time, but soon pro- 
duces unconsciousness and asphyxia, probably because it unites 
so firmly with the hemoglobin of the corpuscles. Hydrogen may 
be inhaled with impunity if it contain also oxygen in the atmos- 
pheric proportion. Carbon monoxide is poisonous because it 
unites with hemoglobin to the exclusion of oxygen and will not 
dissociate itself. Sulphuretted, phosphoretted and arseniuretted 
hydrogen are destructive of hemoglobin and consequently poison- 
ous. Pure carbon dioxide cannot be inhaled for any length of 
time. 

Abnormal Respiration. — The term eupnea is used to describe 
normal, tranquil breathing. Apnea is suspended respiration. 
Hyperpnea is exaggerated respiration. Dyspnea is labored 
breathing. Asphyxia is essentially a want of O characterized 
by convulsive respirations, and later by irregular shallow breath- 
ing. The last two named deserve some attention. 

Dyspnea may be due to either a deficiency of O or an excess 
15 



226 



RESPIRATION. 



of C0 2 in the blood. When an animal is made to breathe in a 
small, confined space the amount of O soon becomes insufficient, 
even though the amount of C0 2 in the blood be not increased. 
Again, if an animal be caused to breathe air containing the 
usual amount of O and a large amount of C0 2 , it will suffer 
from dyspnea also. In either case the manifestations are prac- 
tically the same — slow, deep and labored respiration. In car- 
diac disease, hemorrhage, pulmonary diseases, etc., the dyspnea 

Fig. 48. 




The Heart in the First Stage of Asphyxia. 
The left cavities are seen to be distended ; the left ventricle partly overlaps the right ; I. a, 
left auricle; l.v, left ventricle; a, aorta; J>.a, pulmonary artery; p.v, pulmonary vein; 
r.a, right auricle; r.v, right ventricle; v.c.d, descending vena cava; v.c.a, ascending 
vena cava. {Kirkes after Sir George Johnson.) 

is from a lack of O in the tissues, because of enfeebled action 
of the heart, deficient quantity of blood, insufficient exposure 
of the blood in the lungs, etc. 

Asphyxia may be looked upon as exaggerated dyspnea. The 
labored breathing of dyspnea becomes convulsive, and finally 
collapse ensues. Respiration becomes shallow, consciousness 
is lost, the pupils are dilated, opisthotonus develops, the re- 
flexes disappear, and at last the heart stops beating. The skin 



ASPHYXIA. 



227 



and mucous membranes become blue from non-oxygenation of 
the blood. Asphyxia from submersion is harder to overcome 
than from simple deprivation of air outside the water. Resusci- 
tation is extremely doubtful when a person has been submerged 
as long as five minutes. 

While the phenomena of dyspnea and asphyxia are referable 
to the lungs, it is not the need of air in these organs, but of O in 
the tissues, which gives rise to the symptoms. The non-oxygen- 
ated blood in asphyxia will not circulate through the capillaries 

Fig. 49. 




The Heart in the Final Stage of Asphyxia. 
The letters have the same meaning as in Fig. 48; in addition, p.c, represents the pulmo- 
nary capillaries. The right auricle and ventricle, and the pulmonary artery, are fully dis- 
tended, while the left cavities of the heart and the aorta are nearly empty. (Kirkes after 
Sir George Johnson.) 

except with the greatest difficulty, and the result is that it accu- 
mulates in the arterial system, dams back upon and distends the 
heart, so that this organ is finally paralyzed and ceases to beat. 
This is the cause of death from asphyxia. 

Effect of Respiration on Blood-Pressure. — The lowest blood- 
pressure is just after the beginning of inspiration, from which 
time it increases during inspiration to reach its maximum 



228 



RESPIRATION. 



just after the beginning of expiration \ it gradually decreases 
from this time to the minimum just after the beginning of in- 
spiration. The general effect, then, of inspiration is to increase 
blood-pressure and of expiration to decrease it. This remark 
applies to general arterial tension. 

Taking inspiration, the increase in arterial tension is, in its 
last analysis, due to the larger amount of blood sent into the 
arterial system at each ve?iticular systole. The explanation is 

Fig. 50. 



Carotid Blood-Pressure Tracing of Dog. 
Vagi not divided; I, inspiration; E, expiration. {Stirling.') 

somewhat complex, but if the mechanics of respiration be under- 
stood it may be made satisfactory. 

It was seen that the lungs are contained in an air-tight 
cavity, the chest, and that they expand with the chest because 
of negative pressure ("suction") exerted upon them. The 
heart is also a hollow organ situated in this cavity ; it has con- 
nected with it, and lying also in the thoracic cavity, large vessels 
communicating with smaller extra-thoracic vessels. The heart 
and these great thoracic vessels are elastic and distensible. Con- 
sequently the expansion of the thorax also expands them slightly 
and tends to draw blood from the extra-thoracic into the intra- 
thoracic vessels and heart ; in fact inspiration is one of the main 
forces causing a flow of venous blood toward the heart. Now 
all this, so far as it goes, tends to keep the blood out of the 



RESPIRATION AND BLOOD PRESSURE. 229 

extra-thoracic vessels, and so to contradict the statement that 
inspiration increases arterial tension. 

But, remembering that we are dealing with arterial tension 
and that our effort is to prove that more blood is sent into the 
aorta during inspiration than during expiration, it is of value to 
note that since the walls of the aorta are more resistant than 
those of the venae cavae there is less expansion of the former than 
of the latter during inspiration, and consequently less tendency for 
the arterial blood to regurgitate into the thoracic aorta than for 
the venous blood to enter T the thoracic venae cavae. The same 
expanding force dilates the pulmonary capillaries, pulmonary 
artery and pulmonary veins — the artery least of these. Taking it 
for granted that more blood is being received by the right side of 
the heart from the incoming venae cavae, the somewhat dilated 
pulmonary artery receives more from the right ventricle ; the 
pulmonary capillaries are more dilated than the artery and this 
fact greatly encourages (by a suggestive " suction") the in- 
creased flow from the pulmonary artery; they, therefore, receive 
more blood than usual. The pulmonary veins, being likewise 
dilated, exert " suction " upon the capillaries, and thus receive 
and pass on to the heart a larger supply of blood than usual. 
The heart, receiving more blood, must send more into the aorta, 
thereby increasing arterial tension in the extra-thoracic vessels, 
unless, by expansion of the chest, the thoracic aorta be so dilated as 
to acco7nmodate the increased amount — which is not true. 

Then, finally, the validity of this argument will hinge on the 
relative dilatation of the thoracic aorta and of the thoracic venae 
cavae. If the veins be less dilated by inspiration than the artery, 
then they will receive an increase of blood which will not com- 
pletely occupy the increase of space in the dilated thoracic aorta, 
and there will be a backward "suction " made upon the contents 
of the arterial tree with a consequent decrease in pressure ; but 
a condition just opposite to this seems to obtain. 

During expiration contrary conditions in general are operative 



230 RESPIRATION. 

with contrary results. The intra-pulmonary vessels and heart 
are compressed, but the veins and capillaries more than the aorta, 
with the result that less blood reaches the heart than during in- 
spiration, and the thoracic aorta being, relatively to the thoracic 
venae cavae, more dilated now than during inspiration can easily 
accommodate the decreased amount of blood which it receives. 
Of course expiration increases venous pressure in the veins which 
enter the thorax back as far as the valves. 

The reason the pressure does not rise with the beginning of 
inspiration is because a short time is consumed in filling the flac- 
cid intra-pulmonary veins, and the first increase of blood is de- 
layed for that purpose instead of passing on to the left side of 
the heart. Similarly, the pressure continues to rise for a short 
time after expiration has begun because the large veins are being 
emptied by pressure during this time and their contents are 
reaching the heart and being forced into the aorta. 

Movements of the diaphragm and abdominal muscles during 
respiration also lend themselves to create like changes in arterial 
pressure, but the main factors are intra-thoracic. 

The fact that the cardiac rate is increased during inspiration 
and decreased during expiration may also have to do with the 
variations in pressure. 

All the foregoing remarks relative to arterial tension are meant 
to apply to tranquil respiration. During forced inspiration, or 
forced expiration, the results may be modified, or even reversed, 
by circumstances not necessary to mention. 

Nervous Mechanism of Respiration. — Although the muscles 
of respiration are of the striated variety, it is by no effort of the 
will that the movements are kept up. They belong to the class 
known as automatic ; that is, they are, up to certain limits, under 
the control of the will, but recur in a regular, coordinate and 
orderly manner without the active intervention of volition. Res- 
piration represents the activity of a self-governing apparatus. 
These movements constitute a finely coordinated set of contrac- 



RHYTHM OF RESPIRATION. 23 1 

tions — contractions which are regulated by means of afferent 
and efferent nerves under the supervision of the respiratory 
center. 

The respiratory center is in the lower part of the medulla ob- 
longata. Destruction of the encephalon above, or the cord 
below, the center does not arrest respiration. It is bilateral — a 
center for each side — and these are more or less independent of 
each other, but are so intimately connected by commissural 
fibers that any impression made upon one usually produces a like 
effect upon the other. Each half presides over the lungs and 
respiratory muscles of its own side, but acts synchronously with 
its fellow of the opposite side. Furthermore, each of these 
lateral centers may be regarded as consisting of two parts, one 
for inspiration and one for expiration. Stimulation of the in- 
spiratory center not only strengthens the inspiratory act, but also 
accelerates respiration. Stimulation of the expiratory center 
strengthens expiration and also retards the respiratory rate. The 
accelerator portion of the center seems more sensitive than the 
inhibitory, and the result of stimulation of the whole center 
is therefore quickened respiration. 

Subsidiary respiratory centers are said to exist in the tuber 
cinereum, optic thalamus, corpora quadrigemina, pons Varolii 
and spinal cord ; but the existence of at least some of these 
is doubtful. 

Rhythm of Respiration. — What agency excites the center to 
keep up the respiratory movements with such regularity is a 
matter of interest. The chief circumstances which seem to af- 
fect the rate and rhythm are (i) the will, (2) emotions, (3) com- 
Position of the blood and (4) afferent impressions. 

1, 2. The effect of the will and emotions are too apparent 
to call for comment. 1 and 2 are properly included in 4. 

3. A deficiency of O or an excess of C0 2 in the blood will 
increase the rate. Increase in temperature of the blood, as in 
fever, will produce a similar effect. 



232 RESPIRATION. 

4. The most important of these agencies is found in afferent 
impressions conveyed to the center. The fibers carrying these 
impressions are chiefly in the pneumogastric, glossopharyngeal, 
trigeminal and cutaneous nerves. Of these the pneumogastric is 
by far the most important. 

Section of a single pneumogastric is followed by variable 
respiratory disturbances which usually disappear in less than an 
hour. Section of both nerves is followed, after a short interval 
of increased respiratory activity, by slow and powerful inspira- 
tions, by forced expiration and an appreciable interval be- 
fore the next inspiration. Irritation of the central end of the 
cut nerve by a very weak current seems to stimulate the inhibi- 
tory part of the center, for the rate is slowed, the expirations 
are strenuous and the inspirations weak. When the current is 
increased to a moderate strength opposite results are ob- 
tained, the accelerator portion of the center being stimulated. 
These facts show that the pneumogastrics possess both in- 
spiratory and expiratory fibers, and that the former are stimu- 
lated more by a moderate current and the latter more by a very 
weak one. The rhythm of respiration, therefore, includes the 
regular sequence of inspiratory and expiratory movements upon 
each other. 

Now what is it that, under normal conditions, irritates the termi- 
nals of the pneumogastrics and causes them to convey inspiratory 
and expiratory impressions ? It has been held that a change in 
the composition of the alveolar air — an accumulation of carbon 
dioxide — irritates the nerve terminals and explains the convey- 
ance of the inspiratory impressions, while the stretching of the 
lung tissue originates the expiratory impressions. Others ascribe 
both inspiratory and expiratory impressions to lung movements — 
movements of inspiration exciting expiratory fibers, and move- 
ments of expiration exciting inspiratory fibers. These observers 
cite the fact that artificial inflation and aspiration excite expira- 
tion and inspiration respectively. 



NERVOUS CONTROL OF RESPIRATION. 233 

Stimulation of the superior laryngeal, as when foreign bodies 
accidentally enter the larynx, excites violent expiration. 

The glosso-pharyngeal contains afferent fibers especially impor- 
tant in arresting respiration — at any stage whatever — during the 
act of deglutition. 

Stimulation of the sensory fibers of the trigeminal in the nose, 
as by irritating vapors, may arrest respiration. 

Irritation of the cutaneous nerves in general, as by cold or hot 
water, slapping, etc. , stimulates respiratory movements. 

There are, of course, running from the cortex to the respira- 
tory center i?itra- cranial fibers whereby the organ of the will 
makes its presence felt in respiration. 

But when all the afferent nerve connections are severed, 
respiration continues with modified rhythm and rate, at least for 
a time. It is thought that, under these conditions, it is the cir- 
culation through the center of blood deficient in oxygen which 
causes the cells to discharge \ that is, after every inspiration and 
subsequent expiration there is not another inspiration until the 
blood has become sufficiently deoxygenated, or charged with 
carbon dioxide, to irritate the respiratory ceiiter. 

We may conclude that " the rhythmical discharges from the 
center are due primarily to an inherent quality of periodic ac- 
tivity of the nerve cells constituting the respiratory center, and 
maintained by the blood, and that the rhythm, rate, and other 
characters of these discharges may be affected by the will and 
the emotions, by the composition, supply and temperature of the 
blood, and by various afferent impulses. The chief factors are 
the quantities of O and C0 2 in the blood, and the impulses con- 
veyed from the lungs by the fibers of the pn.eumogastric nerves. ' ' 
(Am. Text-Book.) 

The efferent nerves of respiration control the muscular move- 
ments of that act. They are chiefly the facial, hypoglossal and 
spinal accessory controlling the respiratory movements about the 
face and throat • the pneicmogastric going to the larynx ; the 
phrenic to the diaphragm ; certain of the spi?ial nerves. 



234 RESPIRATION. 

To the lungs proper fibers are distributed by the vagus, the 
dorsal spinal and the sy?npathetic nerves. Besides the expiratory 
and inspiratory fibers already noticed, the vagus supplies the 
lungs with broncho-motor, general sensory, trophic and secre- 
tory (mucous) fibers. The sympathetic furnishes trophic and 
vasomotor fibers, which latter come from the cord by the roots 
of the dorsal nerves mentioned to join the sympathetic ganglia. 



CHAPTER VII. 
EXCRETION BY THE KIDNEYS AND SKIN. 



Excretion of the various foods after they have discharged 
their several functions in the body is effected mainly by the 
kidneys, skin, lungs and alimentary canal. The excretory action 
of the last two named is considered under Respiration and Di- 
gestion. Attention is again called to the fact that it is impos- 
sible to differentiate strictly between a secretory and excretory 
fluid. The urine is as typical of the excretions as any fluid to 
be found. But it will be convenient to speak of the " secre- 
tion ' ' of urine when reference is made to the act of separating 
its constituents from the blood. 

The Kidneys. 

Anatomy. — The kidneys, one on each side of the body, are 
behind the peritoneum in the lumbar regions. The right is usu- 
ally a little lower and a little lighter than the left. The hi him 
from which the ureter springs looks inward and forward. The 
kidney, as found behind the peritoneum, is covered with a con- 
siderable amount of fat, but the substance proper of the organ 
is closely surrounded by a somewhat resistant fibrous capsule 
which in health can be easily stripped away. At the hilum the 
capsule is continued inward to line the pelvis, infundibula and 
calyces. 

The kidney belongs to the class of compound tubular glands. 
If it be cut into two halves by an incision passing through the 
two borders (and, therefore, through the hilum) an idea of its 
gross divisions is obtained. The renal substance is seen to be 

235 



236 



EXCRETION BY THE KIDNEYS AND SKIN. 



divided into an outer layer, known as the cortical substance, and 
an inner, or pyramidal, portion. Internally the incision reveals 
a cavity into which the ureter opens. This is the pelvis. 

Tracing the divisions of the pelvis toward the kidney sub- 



Fig. 51. 




Longitudinal Section Through the Kidney, the Pelvis of the Kidney, and a 
Number of Renal Calyces. (From Brubaker, after Tyson.) 

A, branch of the renal artery ; U, ureter ; C, renal calyx ; 1, cortex ; 1 ', medullary rays ; 
1 '', labyrinth, or cortex proper; 2, medulla ; 2', papillary portion of medulla, or medulla 
proper; 2", border layer of the medulla; 3, 3, transverse section through the axes of the 
tubules of the border layer; 4, fat of the renal sinus; 5, 5, arterial branches; * transversely 
coursing medulla rays in column of Bertin. 



STRUCTURE OF THE KIDNEY. 



237 



stance, it is found to be continued by three short canals, one to- 
ward the upper, one toward the lower and one toward the cen- 
tral portion of the organ. These are the three infundibula. 
Each infundibulum, passing outward, subdivides into two or 
three, or more, short cylinder-like canals which receive the 
apices of the pyramids. These are the calyces, each of which 
receives the apex of one or more pyramids. The urine thus 
escaping from the pyramidal tubules passes in succession through 
the calyces, infundibula, pelvis, and thence into the ureter. 




7k> Cortex. 



Boundary or 
7 ^marginal 



£ \ Papillary 
(zone. 



LS, of a pyramid of Malpighi ; PF, pyramids of Ferrein ; RA, branch of renal artery 
with an interlobular artery ; R V, lumen of a renal vein receiving an interlobular vein ; 
VR, vasa recta; PA, apex of a renal papilla; b, b, embrace the bases of the lobules. 
{Stirling,) 



238 EXCRETION BY THE KIDNEYS AND SKIN. 

The cortical substance constitutes the outer layer of the kid- 
ney and is about -i- inch thick. It is reddish and granular in 
appearance. From it pass in between the Malpighian pyra- 
mids columns known as the columns of Bertin. The cortical 
substance contains the glomeruli and convoluted tubules to- 
gether with blood-vessels and lymphatics supported by connec- 
tive tissues. 

The pyramidal substance, also called the medullary sub- 
stance, consists of a number of pyramids, about 12-15, whose 
bases look outward and rest on the cortical substance and whose 
apices look inward and are received into the calyces. These 
are called the pyramids of Malpighi. They contain uriniferous 
tubules, vessels, etc., supported by connective tissue. It will 
be seen that these tubes converge and join each other in passing 
from the base to the apex of the pyramid, so that the very large 
number entering the base is represented by only 10-25 at the 
apex. Thus it is that the Malpighian pyramid is divided into a 
number of smaller pyramids. These latter are the pyramids of 
Ferrein, and correspond in number to the number of tubes radi- 
ating from the apex of the larger pyramid. The medullary 
substance is marked by striae which have the direction of the 
tubules and which are caused by them. Its consistence is firmer 
and its color is darker than that of the cortical substance. 

Malpighian Bodies. — These are scattered throughout the cor- 
tical substance, and are T ^ - -^\-§ inch in diameter. They consist 
of a bunch of capillaries in the shape of a ball, the glomerulus, 
surrounded by the extremity, or rather the beginning, of one of 
the renal tubules. At the point where the tubule joins the Mal- 
pighian tuft it is constricted ; running then over the glomerulus 
it reaches the afferent artery and the efferent vein on the oppo- 
site side ; when it has reached these vessels it is reflected over 
the whole network of capillaries so that really the tuft is outside 
the tube, but practically it is covered by a double layer of the 
tube wall. A space, the beginning of the tubule, is left between 



STRUCTURE OF THE KIDNEY. 



2 39 



these two layers and into it the glomerular secretion passes. The 
outer layer is the capsule of Bowman (or Miiller j. Both layers 
consist of a single stratum of flattened epithelial cells ; those of 
the inner layer are applied closely to the glomerulus and are 
thought to be very important in secretion. The incoming artery 
Fig. 53. Fig. 54. 




Transverse Section of a Developing 
Malpighian Capsule and Tuft 
(Human). X 300. 
From a fetus at about the fourth month ; 
a, flattened cells growing to form the cap- 
sule ; b y more rounded cells continuous with 
the above, reflected round c, and finally en- 
veloping it ; c, mass of embryonic cells 
which will later become developed into 
blood-vessels. {Kirkes after W. Pye.) 



Epithelial Elements of a Malpi- 
ghian Capsule and Tuft. 
With the commencement of a urinary tu- 
bule showing the afferent and efferent vessels ; 
a, layer of flat epithelium forming the cap- 
sule ; b, similar, but rather larger epithelial 
cells, placed in the walls of the tube; c, 
cells, covering the vessels of the capillary 
tuft ; d, commencement of the tubule, some- 
what narrower than the rest of it. {Kirkes 
after W. Pye.) 



breaks up to form the capillary tuft ; the corresponding outgoing 
vein has a smaller caliber than the artery. The vein, having 
left the glomerulus, breaks up into a secondary network around 
the convoluted tubes. This arrangement of the Malpighian body 
furnishes a most favorable opportunity for the passage of sub- 



240 EXCRETION BY THE KIDNEYS AND SKIN. 

stances out of the blood current into the beginning of the 
tube. 

Uriniferous Tubules. — These begin at the glomeruli and end 
at the apices of the Malpighian pyramids. From their tortuous 
course in the cortical portion they are there called convoluted 
tubules, in contradistinction to the straight tubes of the medullary 
portion. This, however, is only a general division ; further 
the distinctions are to be noted. 

The constricted portion of the tube where it leaves the glomer- 
ulus is the (1) neck; passing away from the neck the tubule 
becomes very tortuous and is known as the (2) primary convo- 
luted tubule, which, having run for a variable distance, becomes 
narrow near the base of the pyramid, and taking a comparatively 
straight course downward enters the pyramid under the name of 
the (3) descending limb of Henle's loop; some of these run 
nearly as far as the apex, but most of them near the base or 
middle of the pyramid turn upward forming thus (4) Henle* s 
loop and beginning the (5) ascending limb of Henle's loop; 
the tube having reentered the cortical substance becomes con- 
voluted again, (6) secondary convolution, which, by a less 
tortuous continuation, the (7) intermediate tube, communicates 
with the collecting tubules, or the (8) straight tubes of Bellini ; 
these last beginning in the cortex, and receiving in their course 
large numbers of intermediate tubes, enter the base of the pyr- 
amid and run in a nearly straight direction toward the apex. 
About 100 of these straight tubes entering at the base join in 
their course downward until at the apex they are represented by 
a single tube. These collections constitute the pyramids of 
Ferrein ; there are about 12-18 pyramids of Ferrein to each 
Malpighian pyramid, and as many tubal orifices at the apex. 
The so-called zigzag and spiral tubules are here considered parts 
of the first and second convoluted tubules. (See Fig. 55.) 

Before they reach the collecting tubules the tubes vary in diam- 
eter from y-oV 0" t0 woo" ^ ncn > tne collecting tubules progressively 



Fig. 55. 




A Diagram of the Sections of Urintferous Tubes. 
A, cortex limited externally by the capsule ; a, subcapsular layer not containing Malpi- 
ghian corpuscles; a' , inner stratum of cortex, also without Malpighian capsules; B, bound- 
ary layer; C, medullary part next the boundary layer; i, Bowman's capsule of Malpighian 
corpuscle; 2, neck of capsule; 3, first convoluted tubule; 4, spiral tubule; 5, descending 
limb of Henle's loop ; 6, the loop proper ; 7, thick part of the ascending limb ; 8, spiral part of 
ascending limb ; 9, narrow ascending limb in the medullary .ray ; 10, the zigzag tubule ; n, the 
second convoluted tubule ; 12, the junctional tubule ; 113, the collecting tubule of the medullary 
ray ; 14, the collecting tube of the boundary layer ; 15, duct of Bellini. {Kirkes after Klein. ) 
l6 



242 EXCRETION BY THE KIDNEYS AND SKIN. 

increase in diameter from -g-i-^ to ^-g inch. The cells lining 
the convoluted and intermediate tubules are inclined to the 
pyramidal shape. Their bases present the appearance of fibers 
at right angles to the basement membrane (hence " rod- 
ded" cells), while their opposite extremities are granular. 
The tubes of Henle are lined by flattened epithelium for the 
most part. 

The division is somewhat arbitrary, but the secreting portion 
of the tubules is supposed to be confined to the cortical substance, 
while the tubes of the medullary substance only carry away the 
fluid. 

Blood Supply. — The renal artery, having entered the hilum, 
divides into branches, two of which usually enter each column 
of Bertin. Running upward in these columns the branches give 
off small arterial twigs to the substance of the column. When 
a point opposite the bases of the Malpighian pyramids is reached 
each branch follows the convex base of the pyramid to which it 
is adjacent, the one branch going in an opposite direction to 
the other. Each meets a corresponding branch from the other 
side of the pyramid, and thus a convex arterial arch covers 
the base of the pyramid, from which arch branches go in- 
ward to supply the medullary substance and outward to furnish 
branches to the glomeruli. The arrangement of the vessels in 
relation to the Malpighian bodies has been noticed. In the 
glomerulus the capillaries do not form a true anastomosis, 
but this is not true of the network surrounding the convoluted 
tubes. 

Mechanism of Urinary Secretion. — Histologists have been 
unable to demonstrate the presence of distinct secretory fibers 
for the glomerular or tubal cells. This leaves the mechanism of 
secretion to be explained by (1) the vascular supply and by (2) 
the " vital activity " of the cells — both operating in conjunction 
with osmosis. 

Irritation of a certain part of the floor of the fourth ventricle 



STRUCTURE OF THE KIDNEY. 



243 



occasions certain marked changes in the quantity and quality of 
the urine ; section of the upper dorsal cord temporarily arrests 
the secretion ; mental emotions, such as fright, anxiety, etc., also 




Blood-Vessels of the Kidney. 
A, capillaries of cortex ; B, of medulla; a, interlobular artery ; 1, vas affereus ; 2, vas 
efFerens ; i, e, vasa recta ; VV, interlobular vein ; S, origin of a stellate vein ; i, i, Bowman's 
capsule and glomerules ; P, apex of papilla ; C, capsule of kidney ; e, vasa recta from lowest 
vas efferens. {Stirlifig.) 



244 EXCRETION BY THE KIDNEYS AND SKIN. 

modify the flow. All these circumstances, and many others, 
indicate some control over the activity of the kidneys by the 
nervous system ; but that influence is probably exerted only 
through vaso-constrictor and vaso-dilator fibers to the vessels. 

Assuming for the present that nearly all the constituents of 
urine preexist in the blood and are simply taken out of the cir- 
culation in the kidney, it may be stated that, for most part, the 
water and inorganic salts are extracted by the cells of the Mal- 
pighian bodies, while the urea and related organic solids are 
removed by the cells of the convoluted tubes ; so that the 
specific gravity of the fluid is raised in passing down the tubes. 
While the histology of the kidney, and especially the arrange- 
ment of the glomeruli, is most favorable for the exercise of 
simple osmosis, and while this process is doubtless mainly re- 
sponsible for the phenomena which occur, it seems highly prob- 
able that the cells themselves modify osmotic action by taking 
an active part in the secretion of urine. They undoubtedly 
exercise a selective affinity accounting for the different materials 
handled by the glomeruli and the tubes. Moreover, morpholog- 
ical changes in the tubal cells during activity have been micro- 
scopically demonstrated. Vesicles are described as forming 
in the body of the cell, approaching the lumen, bursting and 
discharging their contents, — which are supposed to include the 
urea and such other materials as may be here extracted from 
the blood. 

As regards the elimination of water and inorganic salts by the 
glomerular epithelium, it must also be admitted that the cells 
take some obscure but active part. Were this only an osmotic 
process the amount eliminated would vary exactly as the pres- 
sure. While usually a rise in renal blood-pressure is accom- 
panied by an increased flow of urine and a fall by a correspond- 
ingly decreased flow, the rule does not always hold good. For 
instance, compression of the renal vein raises the pressure but 
does not increase the amount of urine. 



URINE. " 245 

Another fact, which seems almost if not quite as invariable as 
the effect of blood-pressure, is that the amount of urine varies 
directly as the amount of blood passing through the kidney, in- 
dependently of the pressure ; and these two facts constitute about 
all that is definitely known concerning the local conditions 
affecting the amount of urine. Whether diuretics increase the 
urinary flow by simply drawing water from the tissues into the 
blood and thus increasing the amount and pressure, or by stim- 
ulating the cells of the glomeruli to increased functional activity 
is a matter as yet undetermined. 

Properties and Composition of Urine. — When an ordinary 
amount of liquid is ingested and when the skin is moderately 
active the urine, in normal conditions, has a clear reddish am- 
ber color and a specific gravity of about 1020. The more fluid 
ingested the paler will be the color and the lower the specific 
gravity \ the more active the skin the higher will be the color 
and specific gravity. The urine is diluted in the first case and 
concentrated in the second. The fact is, the amount of solids 
(represented by urea) to be eliminated in 24 hours remains 
approximately the same, and those solids will cause a high or low 
specific gravity according as little or much water is eliminated 
with them. The average amount of urine for a day is 2 or 3 
pints. Normally it has an acid reaction from the presence, not 
of a free acid, but of acid salts — chiefly acid sodium phosphate. 
The odor is not disagreeable on ejection, but decomposition 
soon begins and a characteristic offensive, ammoniacal odor 
develops. 

The kidney is the most important excretory organ in the body 
and the large number of urinary constituents is not surprising. 
The chief organic constituents are urea, uric acid, hippuric acid, 
xanthin, hypoxanthin, creatinin, phenol, indican, oxalic acid, 
lactates, etc. The phosphates ', nitrates, sodium chloride, and car- 
bon dioxide are the chief inorganic materials. 

Urea is the most important of the organic constituents. It 



246 EXCRETION BY THE KIDNEYS AND SKIN. 

contains a large amount of nitrogen. Nearly all of it is re- 
moved from the body by the kidneys, and double nephrectomy 
means death from its retention. Its formation is constant and 
its removal necessary. Its presence in the blood seems to be 
the normal stimulus exciting the activity of the cells of the con- 
voluted tubes. 

Whether urea is produced directly in the tissues, or whether 
only certain substances antecedent to it are there formed, it 
cannot be doubted that it is the chief final product of nitroge- 
nous ingesta and nitrogenous disassimilation. It is practically 
the only way in which the nitrogen of proteid foods can escape 
from the body. It exists not only in the blood but in the 
lymph, vitreous humor, sweat, milk, saliva, etc. It has been 
stated that the taking of large quantities of liquids lowers the 
specific gravity of the urine by diluting it ; this is true, but the 
actual amount of urea is increased somewhat by such a procedure. 
It is not surprising that the quantity of urea is largely increased 
when much nitrogenous food is taken, and that it is greatly de- 
creased by an exclusively vegetable diet. Anything, like exer- 
cise, which will increase actual tissue metabolism, will increase 
the output of urea, while anything retarding tissue metabolism, 
like alcohol, will decrease the output. The average amount of 
urea for 24 hours is 350 to 450 grains. 

Formation of Urea. — Seeing that urea is the typical end prod- 
uct of the physiological oxidation of the proteids, it becomes of 
interest to determine, if possible, where urea formation takes 
place. It is known that the liver is very active in producing 
this substance ; but it is not alone by this organ that urea is 
formed. At the present time the prevailing opinion is that, for 
the most part, the proteids under destructive metabolism in the 
tissues do not reach the urea stage of transformation, but are 
converted into ammonia compounds (which differ very slightly 
from the urea in chemical composition), and these compounds 
are conveyed by the blood to the liver, where the slight 



URIC ACID. . 247 

change necessary to make them urea is effected under the in- 
fluence of this organ. Ammonium carbai?iate seems the typical 
compound, but ammonium carbonate and others are probably 
likewise converted. Artificial circulation of these compounds 
through the liver gives rise to urea ; removal of the liver in- 
creases the ammonia compounds and decreases the urea in the 
urine \ ammonia compounds are normally very much more 
abundant in the portal blood than in the arterial, but when the 
liver is removed they are evenly distributed throughout the cir- 
culation, and the animal dies in a few days of symptoms which 
can be aggravated by administration of the ammonia compounds ; 
— all of which circumstances go to show that it is ammonia com- 
pounds which the tissues produce, and that they are changed to 
urea in the liver. 

Still, removal of the liver does not suspend entirely the out- 
put of urea. Consequently this substance must be formed 
elsewhere, but by what organs is unknown. It is not impossible 
that it is formed to some extent in all organs where proteid 
dissociation is progressing. This is practically, if not really, 
the case in health at any rate, even under the theory above 
mentioned. 

It is to be noted that urea is not fully oxidized ; it can be 
oxidized outside the body. Thus the heat-producing capacity 
of the proteids is not completely utilized. If they have been 
broken down in the body into substances simpler than urea, then 
the amount of heat liberated in such dissociation is consumed in 
building up the urea molecule to be discharged. 

Uric acid is combined in normal urine to form the urates of 
sodium, potassium, magnesiicm, calcium and ammoniwn. The 
urate of sodium is by far the most abundant of these, and, be- 
sides urate of potassium, only traces of the others are found. 
Free uric acid in human urine is pathological. The urates, 
like urea, come ultimately from oxidation of the nitrogenous 
constituents of the body. They are not formed in the kidney, 



248 EXCRETION BY THE KIDNEYS AND SKIN. 

but pass out as such from the blood. About g-14 gr. are dis- 
charged daily. The amount is increased in gout. 

In some animals uric acid takes the place of urea, none of the 
latter being formed. In these cases it is manufactured by the liver 
from ammonia compounds. This does not, however, seem to be 
the origin of uric acid in human urine. It has been looked upon 
as unconverted urea, i. <?., as a product antecedent to urea; but 
at present such does not seem to be the case. A theory that it 
is the end product of the destruction of certain materials in the 
nuclei of cells has considerable support. 

Hippuric acid exists in the urine as hippurates. It differs 
from most of the other urinary constituents in being formed in 
the kidney ; it does not preexist in the blood. The daily output 
of this substance is about 10 grains, though the amount may be 
considerably increased on a vegetable diet. The benzoic acid 
of vegetables seems to be synthesized into hippuric. In proteid 
disassimilation some benzoic acid may be produced and elimi- 
nated in this shape. 

The various lactates are not formed by the kidney, but pass 
unchanged into it from the blood. The lactic acid from which 
they are formed probably results from the transformation of 
dextrose. 

Creatinin is normally present in the urine. It is a nitrog- 
enous body differing from creatin only by a molecule of 
water. It is eliminated to the extent of about 15 grains per 
day. A part comes from proteid destruction in the body, and 
another part is said to come directly, without metabolism, from 
creatin which is a constituent of ordinary meat. It is not formed 
in the kidney. 

Xanthin, hypoxanthin, etc., are to be regarded as organic 
nitrogenous excreta allied to uric acid and resulting in some way 
from proteid metabolism. They are regarded by some as hav- 
ing the same probable origin as uric acid, viz., the disintegration 
of cell nuclei. 



URINARY CONSTITUENTS. "249 

The inorganic constituents scarcely deserve separate mention. 
It is through the kidney that the largest variety and quantity of 
inorganic materials are discharged. Certain of these are con- 
stant, but the wide variety of such materials taken into the ali- 
mentary canal accounts for the same wide variety in the urine. 
The proportion of inorganic substances in the blood is approxi- 
mately constant — kept so by the removal of any excess by the 
kidneys chiefly. 

Sodium chloride is eliminated thus to the extent of about 151 
grains daily. The sulphates are unimportant. About 25 grains 
are excreted daily. The phosphates are more important, the 
acid sodium phosphate being mainly responsible for the acid re- 
action of the urine. Nitrogen and carbon dioxide are the chief 
gases to be found. The color of urine is due to a substance, 
urochrome, which is probably formed from hemoglobin. Some 
mucus from the bladder is also in the urine. 

Variation in Amount and Composition of Urine. — " Its con- 
stitution is varying with every different condition of nutrition, 
with exercise, bodily and mental, with sleep, age, sex, diet, res- 
piratory activity, the quantity of cutaneous exhalation, and in- 
deed with every condition which affects any part of the system. 
There is no fluid in the body that presents such a variety of con- 
stituents as a constant condition, but in which the proportion of 
these constituents is so variable " (Flint). 

Prolonged bodily exercise will increase the amount of urea, 
but the urine is generally decreased in quantity because perspi- 
ration is more active. The young child discharges relatively 
much more urea and urine than the adult. The female dis- 
charges relatively more urine, but less urea, than the male. 
Digestion increases the urinary flow. Climate and season act 
chiefly through increasing or diminishing cutaneous activity. 
Emotions of various kinds may give rise to an abundant flow of 
pale urine. 

Discharge of Urine. — On leaving the pelvis of the kidney the 



250 EXCRETION BY THE KIDNEYS AND SKIN. 

urine enters the ureters and passes through them to the bladder, 
whence it is discharged per urethram. 

The ureters run, one from each kidney, downward and slightly 
inward behind the peritoneum, a distance of some 18 inches to 
the base of the bladder. In the female the cervix uteri lies be- 
tween the two ureters just before they enter the bladder. They 
penetrate the bladder wall obliquely, their course therein being 
nearly an inch long. The effect of this arrangement is that dis- 
tention of the bladder closes the opening more closely instead 
of causing regurgitation into the ureter. The ureter is com- 
posed of three coats. The outer is fibrous, the middle muscu- 
lar, and the internal mucous. 

The bladder serves as a reservoir for the urine until such time 
as it is convenient for it to be evacuated. This organ, when 
empty, lies deep in the pelvis in front of the rectum in the male 
and of the uterus of the female. When moderately distended 
it will hold about a pint, has an ovoid shape and rises to the 
brim of the pelvis. It also has three coats. The outer is peri- 
toneal, and covers the posterior and small parts of the lateral 
and anterior surfaces only. Its lower limit posteriorly is the 
entrance of the ureters. The middle layer is muscular. The 
fibers, which are non-striped, are disposed in three sheets. Their 
contraction compresses the contents from all directions. Em- 
bracing the neck (outlet) of the bladder is a thick band of plain 
muscle tissue known as the sphincter vesicce. The tonic contrac- 
tion of this muscle prevents the continual escape of urine. The 
inner coat of the bladder is mucous. It is rather thick, and 
loosely adherent to the subjacent muscular coat except over the 
corpus trigonum where it is closely attached. The corpus trigo- 
num is a triangular body of fibrous tissue just underneath the 
mucous membrane \ its apex is at the origin of the urethra, and 
its other angles are at the vesical openings of the ureters. 

Absorption from the intact mucous membrane of the bladder 
takes place very sparingly, if at all. Abrasions of the membrane 



DISCHARGE OF URINE. 25 1 

from any cause allow absorption to occur ; and this fact may be 
made use of to locate lesions giving rise to hematuria. Iodide 
of potassium injected into the bladder can be detected in the 
saliva if the bladder is the source of the blood. 

Micturition. — When the bladder has become moderately full 
the desire to expel its contents arises. The act of micturition 
involves relaxation of the sphincter vesicce and contraction of the 
muscular walls of the bladder aided by the abdoi7iinal muscles 
and those of the urethra. A slight contraction of the abdomi- 
nal muscles compresses the bladder ; after a short interval the 
sphincter relaxes and allows the stream to pass out through the 
urethra. When the act has been begun contraction of the blad- 
der will suffice to nearly empty the organ, but complete evacu- 
ation is finally brought about by a series of convulsive contrac- 
tions on the part of the muscles of the abdomen. 

The center controlling the reflex nervous phenomena of mic- 
turition is opposite to the fourth lumbar vertebra in the spinal 

cord. 

The Skin. 

Functions. — The functions of the skin from a physical stand- 
point are sufficiently apparent. It furnishes protection to the 
underlying parts, preserves the general contour of the body, 
affords lodgment for afferent nerve terminations, and thus estab- 
lishes relations between ourselves and our surroundings. As an 
organ of excretion it is very important, and in fact essential to 
life. While various organic and inorganic materials, such as 
urea and C0 2 , are thus discharged from the body, their amount 
is more or less inconsequential, and it appears that it is the action 
of the skin as a regulator of heat " excretion " which is vital. 
It furnishes one of the three chief routes for the discharge of 
water from the body, and it will be seen that it is largely through 
the output of water that the output of heat is regulated. So 
necessary is the skin in this respect that the covering with im- 
permeable substances of as much as half the body surface is fol- 
lowed by t death. 



252 



EXCRETION BY THE KIDNEYS AND SKIN. 



The skin excretions are contained in the products of the se- 
baceous and sweat glands. These products correspond altogether 
to neither the secretions nor the excreti'ons, and the sebaceous 
glands have been described under the head of secretion. It is 
to be remembered, however, that the sweat usually represents part 

Fig. 57. 




Stratum corneum. 



Stratum lucidum. 



Stratum granulosum. 



"' ' (^-/•'•''■- Stratum Malpighii. 






J 



Vertical Section of the Human Epidermis. 
The nerve-fibrils, n, b, stained with gold chloride. {Landois.) 

of the sebaceous as well as the sudoriparous secretion, because 
the mixture of the two is a physical necessity. It is the water of 
the sweat which is the most important excretion from the skin, 
although the elimination of C0 2 and inorganic salts, and 



STRUCTURE OF THE SKIN. 2*53 

especially of urea in some pathological conditions, is not to be 
overlooked. 

Structure, — The skin consists of an external covering, the 
epidermis, with its modifications, hair and nails, and of the cutis 
vera. Imbedded in the cutis vera are sebaceous and sweat gla?ids 
and hair-follicles. (Fig. 58.) 

Epidermis. — The epidermis consists of at least four layers of 
epithelial cells. From above downward these are (i) the 
stratum corneum, (2) the stratum luciditm, (3) the stratum 
granulosum, (4) the rete mucosum or Malpighii. All these except 
the stratum corneum have a fairly constant thickness. The 
stratum corneum is thick or thin according to location and de- 
gree of exposure, and its cells are flat and horny. The lowest 
cells of the rete mucosum are columnar. From this last-named 
layer the cells pass gradually upward, and as gradually assume 
the shape of the horny layer. The horny cells are thrown off 
and their place is taken by others from beneath. (Fig. 57.) 

Hairs are to be found on almost all parts of the cutaneous 
surface. They consist of a bulb and a shaft. A depression of 
the skin involving both epidermis and cutis vera constitutes the 
hair-follicle in which the bulb rests. A projection at the bottom 
of the follicle corresponds to a papilla, and upon it the bulb 
is placed. The shaft has an oval shape in cross section. It is 
composed of fibrous tissue, outside which is a layer of imbricated 
cells. 

Nails consist of a superficial layer of horny cells and a deeper 
one corresponding to the rete mucosum. The root of the nail 
is received into the matrix — a specialized portion of the cutis 
vera. 

Cutis Vera. — The cutis vera is tough but elastic. It rests upon 
cellular and adipose tissue. Its structure is areolar with some 
non-striated muscle fibers. Projecting from the cutis vera into 
the epidermis are minute conical elevations, the papillce. Many 
of them contain sensory nerve terminals. 



254 



EXCRETION BY THE KIDNEYS AND SKIN. 



Sweat Glands. — Practically the whole cutaneous surface con- 
tains sweat glands. Some two and a half millions are thought to 
exist in the skin of the average individual. They are particularly 

Fig. 58. 




Vertical Section of Skin. 

A, sebaceous gland opening into hair-follicle; B, muscular fibers; C, sudoriferous or 
sweat-gland; D, subcutaneous fat; E, fundus of hair-follicle, with hair-papilla. (Kirke 
after Klein. ) 



SECRETION OF SWEAT. 255 

abundant in the skin of the palms of the hands and soles of the 
feet. They belong to the simple tubular type, and consist of a 
secreting portion and an excretory duct. The secreting part lies 
just underneath the true skin and, as a whole, resembles a small 
nodule ; however, the nodule consists of an intricate coiling of 
the tube itself which is of tolerably uniform diameter throughout. 
It curls upon itself some 6-12 times and ends by a blind ex- 
tremity. It is lined by epithelial cells. 

The duct passes away from the glandular coil, runs through 
the cutis vera in a comparatively straight course and assumes a 
spiral shape as it traverses the epidermis to open obliquely on 
the surface. With the ducts of the larger glands are connected 
a few non-striped muscular fibers which may aid in the discharge 
of the secretion. (Fig. 58.^ 

Properties and Composition of Sweat. — The secretion is 
colorless, has a slight characteristic odor, and a salty taste. Its 
specific gravity is about 1003-4, and its reaction is usually acid 
when just discharged. It contains a large proportion of water, 
a little urea and fatty matter, and quite a quantity of inorganic 
salts of which the chief is sodium chloride. All the constituents 
in health are of subsidiary importance except the water. Under 
average conditions of temperature and exercise the amount se- 
creted in 24 hours is about 2 pounds. But the quantity is very 
variable — as much so as the urine, and may be said in a general 
way to vary inversely as the urinary secretion. 

Mechanism of the Secretion of Sweat. — Sweat is produced 
continuously, though up to a certain point it passes off as vapor, 
or " insensible perspiration. ' ' Beyond that point it accumulates 
on the skin as an evident fluid and becomes "sensible perspira- 
tion." Whether it escape as sensible or insensible perspiration, 
it is secreted as a fluid. 

The activity of the cells lining the glandular coils in separat- 
ing sweat from the blood is undoubted. Distinct secretory fibers 
are distributed to them, and through the influence of these fibers 



256 EXCRETION BY THE KIDNEYS AND SKIN. 

the glands will secrete sweat even without an increase in the 
blood supply. But usually a determination of blood to the sur- 
face means an increase of perspiration. This occurs during vio- 
lent exercise, e. g. However, that the production of sweat is not 
altogether dependent on this factor is shown by profound sweat- 
ing in shock, nausea and like conditions when the skin is pale 
and cold, and by dryness of the flushed skin in febrile diseases. 
Furthermore, experiments on inferior animals have revealed 
fibers which influence the secretion of sweat without affecting the 
blood flow. 

Practically, in health, the only conditions which increase the 
flow of perspiration are muscular exercise and a high external 
temperature. Of these, exercise probably works through the 
nerve centers ; external heat does not stimulate the glands 
directly, but irritates the cutaneous terminations of afferent 
fibers which convey impressions to the sweat centers, whence 
messages are sent out by secretory fibers to the glandular epithe- 
lium and their activity begins. In both cases there is accom- 
panying dilatation of the superficial vessels under the influ- 
ence of the vaso-dilator fibers. 

It is supposed that the chief center is in the medulla oblongata 
and that secondary centers exist in the lumbar region of the cord. 

The amount of C0 2 eliminated by the skin is inconsiderable 
in the human being. 



CHAPTER VIII. 
NUTRITION, DIETETICS AND ANIMAL HEAT. 



(A) NUTRITION. 

All the processes which have so far been considered — diges- 
tion, absorption, secretion, circulation, respiration, etc. — have 
a single object, viz., the nutrition of the cells of the body. 

The ultimate source of all nutriment is, of course, food and 
oxygen. The oxygen has been followed from the lungs to the 
tissues as oxyhemoglobin of the blood. The various foods have 
been seen to disappear from the digestive tract and to be con- 
veyed to the tissues by the great nutritive fluid, some in recog- 
nizable and some in unrecognizable form. If, now, we shall be 
able to discover in what way these different materials thus fur- 
nished the cells are utilized and appropriated by them, and in 
what condition they subsequently escape from the system, the 
study of nutrition will have been rendered much clearer. The 
intake is through the lungs and alimentary canal \ the output is 
mainly by the lungs, skin, kidneys and intestines. To show for 
the changes which take place while the food is in the body there 
is the growth of the body, the maintenance of tissue integrity, 
secretion, heat, motion and nervous energy. 

It may be said at once, however, that the exact method of 
appropriation of nutritive material by the tissues is a subject of 
speculation, since it involves the question of life itself; and we 
shall have to be content with recounting some of the conditions 
influencing and some of the phenomena attendant upon the 
process. 

Metabolism. — The general process of nutrition involves 
17 257 



258 NUTRITION, DIETETICS AND ANIMAL HEAT. 

breaking down and building up ; it is both destructive and con- 
structive. It may be said that no cell at two different periods 
of its existence is made up of exactly the same intrinsic particles. 
Some of its substance is continually reaching the worn-out stage, 
becomes effete and must be discharged. To take its place other 
material must be appropriated and built up into an essential part 
of the substance of the cell. The changes — of destruction and 
construction, of disassimilation and assimilation — are described 
under the term metabolism, which means "change." It is evi- 
dent that constructive metabolism (anabolism) and destructive 
metabolism (katabolism) are directly opposite processes. Met- 
abolic activity is certainly influenced, and largely governed, by 
certain physical, chemical and electrical laws, but they are in- 
sufficient to explain all the attendant phenomena. 

Problems Involved in the Nutritive Process. — Since the actual 
changes occurring and the method of their production cannot 
be understood, the question of nutrition resolves itself into a con- 
sideration of the final fate of the various aliments, of their rel- 
ative value in nutrition, of conditions influencing the process, 
and of the explanation of certain facts connected with the de- 
struction of the food-stuffs, particularly the production of heat. 

The change which the foods finally undergo in the body is 
one of oxidation. It is therefore chemical changes which give 
rise to physical activity. Oxidation is accompanied by the pro- 
duction of heat. The same sum total of heat is developed when 
a piece of iron rusts completely away in five years as when it is 
consumed in an atmosphere of oxygen in five minutes. In both 
cases it is oxidized. In the cell oxidation is continually going 
on with the production of heat and of certain excrementitious 
(oxidation) products depending on the kind of proximate prin- 
ciple oxidized. 

Fate of Different Foods in the Organism. — In the first place, 
the foods may be divided, into (I.) those which pass through the 
orga/iism unchanged and (II.) those which lose their identity and 



FOODS IN NUTRITION. - 259 

are discharged as bodies different from those which entered. The 
first class includes the inorganic foods ; the second the organic 
nitrogenized and non-nitrogenized. 

(I.) Attention has been given to the inorganic foods where 
they are discussed as binary proximate principles. Reference 
should be made to p. 19 et seq. for a discussion of the most im- 
portant of them. 

Only a few undergo in the body reactions which alter their 
identity. They may be regarded as already digested and, in fact, 
when dissolved, ready for discharge from the body. They are, 
however, useful and necessary constituents of the body, and if 
they do not take a considerable active part in nutrition, their 
favorable influence on that process makes them essential to 
health. The inorganic foods may be dismissed with a repeti- 
tion of the statement that they are largely introduced in connec- 
tion with the proteid foods from which they cannot be separated 
without destruction of the proteid molecule. Indeed, all the 
proteid food introduced, whether animal or vegetable, contains 
inorganic constituents as a part of the molecule, and these seem 
as necessary to nutrition as do the organic constituents. The 
inorganic and organic enter, are deposited, and seem to be dis- 
charged together. The few reactions which the inorganic foods 
undergo in the body do not materially affect the supply of 
energy. 

(II. ) The p'oteids, carbohydrates and hydrocarbons are all con- 
sumed in the organism, none (unless they have accidentally es- 
caped digestion) being discharged as they entered. 

1. The nitrogenous foods are changed into peptones in the 
alimentary canal, undergo some unknown change in their ab- 
sorption therefrom, appear in the blood as the proteid constitu- 
ents of that fluid, and are offered to the tissues through the me- 
dium of the lymph. The complex proteid molecule is broken 
down into simpler but more stable ones. These end products 
are carbon dioxide, water and urea, together with some sulphates 



260 NUTRITION, DIETETICS AND ANIMAL HEAT. 

and phosphates, the production of which is comparatively imma- 
terial. The urea is distinctive. Heat, which is equivalent to 
so much energy, is evolved in the oxidation process. 

It is probable that not all the proteid, under the ordinary diet, 
is actually built up into celL substance. A part of it seems 
to be destroyed without being transformed into protoplasmic 
material, but the destruction always takes place through the 
agency of the cells, and the end products are always the same, 
whether disassimilation of the proteid occurs with or without its 
becoming an intrinsic part of the cell. 

Nitrogenous Equilibrium — Circulating and Tissue Proteid, — 
The fact, however, that the characteristic function of the ni- 
trogenous foods is to furnish protoplasmic material should not 
be lost sight of. A certain amount is necessary to maintain 
"nitrogenous equilibrium"; that is, to keep the intake of 
nitrogen up to the output. When nitrogenous food is with- 
drawn there continues to be a discharge of urea, which is the 
chief nitrogenous excretion and the amount of which represents 
the amount of nitrogenous disassimilation in the body. The 
urea eliminated under these conditions must represent the actual 
destruction of cell substance, and, since the supply is zero and 
the output is considerable, there is not a state of nitrogenous 
equilibrium ; the animal is suffering destruction of its proto- 
plasm without a compensatory constructive process. On the 
other hand, the supply of nitrogenous material may be, and usually 
is, in excess of the demands of the cells for the actual regener- 
ation of their substance. This excess may be termed " circu- 
lating proteid r ," and is that just referred to as being oxidized 
under the influence of the cells, but without being transformed 
into protoplasm. That part of the nitrogenous supply which 
is built up into a part of the cell has been called " tissue pro- 
teid. ' ' Whether any given molecule of proteid food pass through 
the system as circulating or tissue proteid is only an accident — 
provided the supply be above the demand of the cells for tissue 



FOODS IN NUTRITION. . 26 1 

proteid ; these demands are the first to be supplied by the nitrog- 
enous material at hand. 

From this it is not to be inferred that the exigencies of nutri- 
tion will be met as well without as with circulating proteid. 
When the diet consists of just enough proteid to supply the 
tissue wastes and of ample carbohydrate and hydrocarbon ma- 
terials, the nutritive process is impaired. It seems necessary to 
perfect health that the supply of nitrogenous food be sufficient 
to allow for the oxidation of some of it as circulating proteid in 
a manner analogous to oxidation of the non-nitrogenized organic 
materials. Life can be maintained on nitrogenous food alone, 
but it is obvious that when this is done the amount of circulat- 
ing proteid must be enormously increased so that it may be oxi- 
dized to furnish energy for the body ; for those substances, the 
oxidation of which corresponds to oxidation of the circulating 
proteids and which furnish the main supply of energy for doing 
work (viz., the carbohydrates and hydrocarbons), are now with- 
drawn from the economy. It follows, conversely, that the in- 
gestion of carbohydrates and hydrocarbons lessens the amount 
of proteid necessary to nutrition. 

The albuminoids, such as gelatin' (not meant to be included 
under the term " nitrogenous ' ' foods, though they contain nitro- 
gen), cannot take the place of tissue proteid ; they may be burnt 
in lieu of the circulating proteids and supply energy just as the 
and carbohydrates and fats do. They differ in this respect from 
the organic non-nitrogenous foods, but cannot sustain life. 

It is to be remembered that any excess of proteid or albumi- 
noid food is not discharged as such in the excreta, but undergoes 
oxidation, the end products of which are always the same, water, 
carbon dioxide and urea, or related substances ; the development 
of heat is also an invariable accompaniment of their destruction. 

While a person may live on proteid food, the amount nec- 
essary taxes the digestive and excretory organs to such an ex- 
tent that life is probably shortened. Since the total amount of 



262 NUTRITION, DIETETICS AND ANIMAL HEAT. 

urea is discharged by the kidney, that organ, under an excess of 
proteid diet, is particularly prone to degenerative changes of a 
most serious nature. 

2. The carbohydrates enter the blood from the alimentary 
canal as dextrose, are conveyed to the liver and converted 
into glycogen, which is stored up there to be dealt out to the 
blood gradually, after being reconverted into dextrose. Dextrose 
exists in the blood for a short time only, being converted into 
other substances, but its final oxidation is effected by the tissues. 
Its end products are carbon dioxide and water, with heat. Sugar 
(dextrose) injected into the blood soon disappears. It is thought 
by some to be converted into alcohol in the blood and then 
oxidized. At any rate, the formation of the end products just 
mentioned is the final fate of the carbohydrates, through what- 
ever splitting processes the sugar molecule may pass before it is 
converted into these substances. 

The removal of the pancreas occasions diabetes mellitus, and 
the inference is that this gland gives off to the blood some internal 
secretion which splits up the sugar molecule in the blood. How 
this lesion causes the disease in question is not clear, but the 
retention of a small part of the gland enables the oxidation of 
sugar by the tissues to proceed in the proper way and it is not 
discharged in the urine. 

Value of the Carbohydrates in Nutrition. — The distinctive 
function of the carbohydrates is to act as fuel for the body ma- 
chine ; they are burnt up to supply heat, and heat represents 
energy. Hydrogen and oxygen exist already in the proportion 
to form water — one of the end products — and only enough O 
is required to unite with the carbon of the carbohydrates to form 
C0 2 — the other end product. The burning (oxidation) of a 
carbohydrate outside the body results in the formation of C0 2 
and H 2 and the elimination of heat, which last, if properly 
utilized, can be converted into energy — the power to do work. 
The result of the oxidation of a carbohydrate in the body is the 



FOODS IN NUTRITION. 263 

same. Since this class of food is easily handled by the alimen- 
tary canal, requires little extra O for its destruction, and is very 
abundantly supplied by the vegetable world, it is the most eco- 
nomical from digestive, absorptive, respiratory and financial 
standpoints. Carbohydrates may also be deposited as adipose 
tissue as will be seen presently. 

3. The fats have the same general office in nutrition as the 
carbohydrates, viz., the furnishing of energy by their oxida- 
tion. They leave the alimentary canal by way of the lac teals, 
are conveyed by the blood to the tissues and there oxidized 
with the formation of carbon dioxide and water and the liberation 
of heat. Though more O is necessary to burn up the fat than 
the carbohydrate molecule, oxidation of the fat is attended 
with the liberation of the greater amount of heat — u e., of 
energy. This would seem to indicate that it would be more 
economical to eat fats to the exclusion of carbohydrates, since a 
smaller quantity of the former will supply the requisite amount 
of energy. This is theoretically true, but considerations of di- 
gestion render it not practically so ; fats tax the digestive appa- 
ratus much more than carbohydrates. 

The fat deposited in the body — the adipose tissue — whatever 
may be its source, is to be looked upon as so much stored-up 
energy. When the supply of blood is cut off it is the first part 
of the organism to be consumed. A fat animal will survive 
starvation longer than a lean one. 

The individuality, the functional activity, and the properties 
involved in regeneration of protoplasm are ultimately depend- 
ent upon its nitrogenoics characters. The other constituents are 
more or less passive. The oxidation of fats and carbohy- 
drates, however, takes place under the influence and through 
the agency of the cells. It is scarcely necessary to add that 
neither fats nor carbohydrates, nor both together, are sufficient 
to sustain life; for life is embodied in protoplasm and protoplasm 
must have nitrogen, which element these foods cannot furnish. 



264 NUTRITION, DIETETICS AND ANIMAL HEAT. 

Formation of Adipose Tissue. — The adipose tissue in the 
body is not the result of direct deposition of the oleaginous 
foods. The amount of fat taken on in a given time by some 
animals, as hogs, is often far in excess of the quantity of fat in 
the ingesta. Adipose tissue is, under normal conditions, the 
result always of changes due to protoplasmic activity. It is 
formed by the tissues chiefly from the carbohydrates, but also to 
a less extent from the proteids. The chemical changes by 
which sugar is converted into fat are as yet undetermined, but 
there are so many evidences of an increase in body fat upon 
an excess of carbohydrate food that the fact itself that this class 
of foods is the main source of fat is no longer disputed. 

As regards the formation of fat ixomproteids, it is thought that 
the molecule is split up into a nitrogenous molecule, which is 
discharged as urea, and a non-nitrogenous, which at once, or 
after undergoing other changes, is deposited as fat. Experi- 
mental observations demonstrate that the liver produces glyco- 
gen on a purely proteid diet. Since glycogen is a carbohy- 
drate, and carbohydrates are the chief source of body fat, 
it is not improbable that the non-nitrogenous molecule of the 
proteid dissociation takes the form of glycogen and is later con- 
verted into fat after the manner, whatever it may be, of the 
glycogen introduced in carbohydrate form. When the carbon 
discharged is less than the carbon ingested the deficit is thought 
to be retained to form fat, which is deposited as a reserve to be 
used whenever its oxidation may become necessary as a supply 
of energy. 

It follows that to reduce body fat the carbohydrates should be 
largely interdicted, while to increase it they should be taken in 
excess. In human beings proper regulation of the diet is more 
efficacious in reducing than increasing the amount of adipose 
tissue. 

Adipose Tissue a Reserve Supply of Energy. — The carbohy- 
drates and fats are preeminently the energy-producing foods, 



CONDITIONS INFLUENCING METABOLISM. . 265 

and of these the carbohydrates, for reasons indicated, are 
the more important. They not only furnish energy which 
is immediately used up in running the machinery of the 
body, but they deposit, or attempt to deposit, a reserve supply 
to protect the proteid portions of the organism against accidents 
of temporary deprivation of food, demands for an unusual 
amount of energy, malnutrition from various causes, etc. — sav- 
ings laid for the proverbial rainy day. This reserve supply 
takes the form first of glycogen, which is soon used up, meeting 
as it were only the demands of the hour, and second of fat, 
which begins to be drawn upon when the glycogen is exhausted, 
and which lasts for a length of time depending upon its 
amount. 

Conditions Influencing Metabolism. — Regular exercise is 
undoubtedly favorable to the nutrition of any part, as, e. g., the 
muscles, the brain, etc. Exercise may mean increased disas- 
similation, but if so it also means increased assimilation. With 
regard to muscular exercise of average severity and reasonable 
duration, the results of cellular activity seem at first a little sur- 
prising, but are really to be expected if the concluding remarks 
of the previous paragraph are true. The amount of urea under 
such exercise is not appreciably increased — which means that 
disassimilation in the protoplasm of the muscle cells is not in- 
creased. This remark holds good, however, only when the sup- 
ply of sugars, starches and fats is abundant ; if they are not 
present in sufficient quantity to meet the increased demand for 
energy-supplying materials, then the proteids must be oxidized to 
furnish it, and the urea discharge is increased. In striking con- 
trast to the constant output of urea is the largely increased out- 
put of C0 2 , representing oxidation of the carbohydrates and 
fats. 

During sleep the nitrogenous output is not materially dimin- 
ished, while that of C0 2 is markedly less. This is explained by 
the fact that there is less energy needed and correspondingly less 



266 NUTRITION, DIETETICS AND ANIMAL HEAT. 

oxidation of the energy-producing materials. Proteid metabo- 
lism is undisturbed. 

A low external temperature does not increase the output of 
urea \ it increases the output of C0 2 . These two facts together 
mean again that only the carbohydrates and fats are being oxi- 
dized in increased amount. This increased oxidation, the effect 
of which is to maintain the normal body temperature, is usually 
dismissed with the statement that it is a reflex nervous act. It is 
claimed by Johannson that the C0 2 output is not increased until 
shivering occurs (Reichert). That being the case, the increase is 
explained on the ground of increased energy and heat production 
incident to muscular exercise, and shivering assumes the dignity 
of a physiological factor in keeping up the temperature of the 
body. This is perfectly reasonable when it is remembered how 
effective active muscular exercise is in keeping the body warm. 
But the fact that a person when cold shivers and is restless invol- 
untarily does not allow us to escape the unsatisfactory "reflex 
action ' ' explanation of the phenomenon in question. Within 
ordinary and reasonable limits proteid metabolism is undisturbed ; 
it is still being protected by the fats and carbohydrates. 

During starvation nothing is supplied from the outside world 
except oxygen, and the animal must live on the materials al- 
ready in his body. The glycogen is first consumed ; it is the 
surplus on hand; but at best it is all gone in a very few days. 
Then the fat stored up as adipose tissue is drawn upon ; it is the 
reserve fund ; but it is likewise soon consumed ; the animal be- 
comes progressively emaciated. When this is exhausted the 
tissue proteid is attacked ; this is the capital and is the last to be 
touched ; but there must be heat and at least some energy, and 
there is no other source. When the proteid capital has at last 
been so impaired that it can no longer furnish heat to maintain 
the body temperature and energy to carry on the necessary or- 
ganic functions, the organism is physiologically bankrupt and as- 
signment follows — death is at hand. 



REQUISITES OF DIET. .267 

(B) DIETETICS. 

The appetite, under normal conditions, may be depended upon 
to regulate both quantity and quality of diet in a fairly satisfac- 
tory manner. Different peoples require different proportions 
and amounts of the proximate principles, and the same is true of 
any given individual for varying conditions of temperature, ex- 
ercise, etc. But in any case the object of eating is to prevent 
the loss, in aggregate, of proteid tissue, fat, etc., — to replace the 
wastes, and that in the most convenient and economical way. 

When the ingesta exceed the excreta the animal is gaining in 
weight ; when opposite conditions obtain he is losing ; when 
there is a balance between the two the body equilibrium is being 
maintained. 

Determination of the Requisites of a Diet. — The usual 
method of determining, in a scientific manner, the requisites of a 
normal diet for persons in general is to estimate the amount of 
the various excretions from the bodies of a limited number of per- 
sons in health, and from this knowledge to calculate the amount 
and kind of food which will supply the demands in the most 
satisfactory way, it being assumed that these excretions represent 
the normal and necessary metabolism going on in the body. The 
results of such examination are found to correspond with the 
actual demands of the system. 

It has been seen that the organism demands some fifteen or 
more chemical elements for use to keep itself in good running 
order ; it has been seen also that its demands, so far as quantity 
is concerned, are chiefly confined to carbon, hydrogen, oxygen 
and nitrogen. The other elements deserve no attention here, 
since they (excepting sodium chloride) are unconsciously intro- 
duced with the ordinary foods in amounts sufficient to satisfy 
the requirements of the system. Moreover, the air we breathe 
and the water we drink furnish an ample supply of hydrogen 
and oxygen when to this supply is added the quota of these ele- 
ments contained in the necessary quantities of other aliments. 



268 NUTRITION, DIETETICS AND ANIMAL HEAT. 

So, therefore, if we can fix upon a diet which will furnish the 
requisite amounts of carbon and nitrogen no attention need be 
paid to the other elements. The supply of the others may be 
said to regulate itself if the supply of carbon and nitrogen be 
regulated. 

The object, then, of food may be said to be the replacement 
of carbon and nitrogen — the carbon and nitrogen in the excreta. 
Of these two elements, carbohydrates and fats will furnish only 
carbon ; proteid food will furnish both. 

Amount of C and N Necessary. — It is found that the daily 
discharge of nitrogen is about 18 grams, and of carbon about 281 
grams. These are the amounts, therefore, which must be sup- 
plied by food. We may accept, as representing the proteid 
molecule in general, the formula C 72 H 112 22 N 18 S. Then it is evi- 
dent that an amount of proteid food which would furnish the 
necessary 18 grams of nitrogen would furnish only 72 grams of car- 
bon — only about one-fourth enough. If, now, the proteid food 
be increased to supply 281 grams of carbon, the system will have 
to handle four times as much nitrogen as it needs ; and this is a 
tax to the digestive apparatus and the excretory organs, partic- 
ularly the kidney — a tax which is rendered unnecessary by the 
availability of the carbohydrates and fats as food. These contain 
abundance of carbon, and it is far better to eat only enough pro- 
teid food to supply the 18 grams of nitrogen, and make up the 
deficit of carbon with non-nitrogenized articles of diet. One can 
supply all the demands by eating nitrogenous food alone, and life 
will be preserved indefinitely perhaps, but the prediction would 
be warranted that in such a case the person would probably die 
prematurely — as a result of kidney or liver disease. 

Articles Which will Supply the Necessary Amounts of C and 
N. — The conclusion (modified) of Moleschott is that the average 
man needs daily about 120 grams of proteid, 90 grams of fat, 
and 320 grams of carbohydrate food, estimated dry; and that 
with this, in the usual state in which such food is taken, he will 



REQUISITES OF DIET. 269 

consume unconsciously, or as a result of craving, some 30 grams 
of salts and 2,800 grams of water. These proportions are sup- 
posed to satisfy the demands of the system in an economical 
way. The estimates of Ranke vary somewhat from this as indi- 
cated in the subjoined table which shows also the balance kept 
up in the body. 

Income. Expenditure. 



Foods. I Nitrogen, i Carbon. Excretions. ; Nitrogen. Carbon. 






Proteid 100 gm. " I5.5gm.. 53-°g m - Urea 31.5 gm.l ; 6 6 

Fat 100 " 0.0 " 79.0 " Uric acid 0.5 " J ^'^ 

Carbohy- Feces I.I IO.84 

drates 250 " 00" 93.0 " Respiration (C0 2 ) 0.0 208.00 

I 15.5 " J 225.0 " 15.5 225.00 



The actual amounts of given substances which it is necessary 
to eat in order to supply the requirements of these estimates 
depend, of course, on the composition of those substances, and 
would have to be settled by reference to a table giving analyses 
of the common articles of diet. Two pounds of bread and y{. 
pound (when uncooked) of lean meat, together with water and 
salt, will supply the demands ; but this is an unusual diet. Or 1 
pound of meat, 1 pound of bread and j£ pound of butter, or 
other fat, with water and salt is probably preferable. 

In any case if nutrition is to be properly performed the diet 
must be varied. It could not be held that the above supply of 
food would keep a person indefinitely in good health. His de- 
mands for nitrogen and carbon are always approximately the 
same, but the organism revolts at being supplied with them from 
exactly the same source for any considerable length of time. 

It need scarcely be added that any condition, such as exer- 
cise, temperature, etc. , which increase the excreta, calls for a 
larger supply of ingesta. Ordinary exercise is allowed for in 
the estimates just given. 



270 NUTRITION, DIETETICS AND ANIMAL HEAT. 

(C) ANIMAL HEAT. 

The Temperature. — The average temperature of the human 
body, taken under the tongue, is 98. 5 ° F. It varies in different 
parts, the mean being about ioo°. The metabolic activity in 
different parts of the body is changeable, and consequently the 
heat production in all parts is not the same. 

The fact that the temperature is nearly identical throughout 
the body is due to the distribution of heat, which distribution is 
mainly effected through the agency of the circulating fluids. 
The rectal temperature is a little higher than that obtained in 
the mouth. The temperature of arterial is higher than that of 
venous blood. The warmest blood is in the hepatic veins ; the 
coolest is that which has just passed through the most exposed 
peripheral parts, as the helix of the ear. The mean body tem- 
perature is a little lower in the morning than in the evening, in 
the female than in the male, on a restricted than on an abun- 
dant diet, in cold than in hot climates, and, in general, in condi- 
tions of diminished than of exalted metabolic activity. 

But in health these variations are of trivial importance and do 
not represent a sweep of more than 2 F. The body temper- 
ature may be looked upon as being a fairly constant quantity. 
It varies scarcely at all with variations of external temperature, 
so long as the heat-regulating apparatus is in order. An external 
(dry) temperature of 212 F., or the extremely low temperature 
of some regions, can be borne with very slight fluctuations in 
the temperature of the body. The actual limits of internal tem- 
perature consistent with the preservation of life are given by 
Flint as 83 ° and 107 ° F. These temperatures cannot be long 
endured. 

The fundamental fact to be kept constantly in mind is that 
there is a continual production and a continual dissipation of 
heat, in ways to be indicated presently. These two processes 
are known as thermogenesis and thermolysis respectively. The 



HEAT AND FORCE. 2 7 I 

preservation of the proper balance between heat production and 
heat dissipation is known as thermotaxis. 

Supply of Heat and its Relation to Force. — It is a matter of 
common observation that the burning (oxidation) of any sub- 
stance, as a piece of wood or an article of diet, is accompanied 
by the evolution of heat. It is also known that heat may be 
converted into force — may be made to do work. The burning 
of a fat or a sugar produces C0 2 and H 2 ; the burning of a pro- 
teid produces C0. 2 and H 2 0, and additional substances. The 
final products, and the amount of heat evolved, are precisely the 
same whether the oxidation be rapid or slow. Now, the oxida- 
tion of food is exactly what occurs in the human organism, 
though that of the proteids is not completely effected \ C0 2 and 
H 2 are produced from them, and the " additional substances " 
mentioned are represented by urea. This process then, is the 
source of body heat. To the supply thus furnished may be added 
a little from reactions between inorganic materials in the body, 
from warm foods and drinks, and from friction in the vessels, 
joints, etc. 

The foods thus possess a certain potential energy, an energy 
which may be converted directly or indirectly into heat, or its 
equivalent. The potential energy of the foods keeps up the 
body temperature and supplies force for doing work. It is con- 
verted into heat and kinetic energy. Kinetic energy is working 
energy, and is represented in the body chiefly by muscular con- 
tractions. But, since this kinetic energy has its source in the 
transformation of proximate principles, and since kinetic energy 
and heat are mutually convertible, it may be assumed that all the 
potential energy of the foods is converted into heat. The kinetic 
energy may be taken as representing so much heat, and the total 
production of heat (including kinetic energy) as representing the 
total production of energy. Or, to state the case differently, the 
potential energy of the food is converted into heat, a part of 
which appears as kinetic energy. ■ By far the largest part of this 



272 NUTRITION, DIETETICS AND ANIMAL HEAT. 

potential energy, however, is converted directly into heat. Not 
more than one-fifth of the heat produced in the body can be 
utilized to do work, and a part of that work is actually converted 
indirectly into heat, and contributes to the total heat of the 
body, by overcoming friction incident to respiration, circula- 
tion, movements of the joints, muscles, etc. 

Potential Value of Foods. — It is estimated that the oxidation 
in the body of one gram of fat produces 9,300 calories of heat, 
1 gram of carbohydrate 4,100 calories, and one gram of proteid 
4,100 calories. These figures represent the potential energy of 
the several foods. Fats, it is seen, produce, weight for weight, 
more than twice as much energy as other foods, but reasons have 
been given why they cannot be used exclusively. 

A calorie is the amount of heat necessary to raise 1 gram of 
water i° C. A grammeter is the amount of energy necessary 
to raise 1 gram 1 meter. Now since heat and work are only 
different forms of energy, these two units — calorie and gram- 
meter — have each equivalents in terms of the other. One calorie 
equals 424.5 grammeters ; that is, the force represented by one 
calorie will raise one gram 424.5 meters. The terms kilocalorie, 
or kilogramdegree, and kilogrammeter are used sometimes, and 
represent 1,000 times the calorie and grammeter respectively. 

Total and Specific Heat. — The temperature of a body indi- 
cates nothing as to the quantity of the heat it contains. The 
degree of heat requires only a thermometer to determine it, but 
the quantity depends on the temperature, the weight and the 
specific heat of the substance in question. 

Specific heat is analogous to specific gravity. Water is taken as 
the standard in both cases. If it require only . 5 calorie to raise 
1 gram of a certain substance 1 degree C, the specific heat of that 
substance is said to be .5. The specific heat of the body is 
. 8 ; that is, whereas it requires a certain amount of heat to raise 
150 pounds of water to a certain temperature, it would require 
only .8 as much to raise a hunran body weighing the same to 



THERMOGENESIS. 273 

the same temperature. To find the total heat in calories in 
any body it is only necessary to multiply the weight (in grams) 
by the specific heat and by the temperature C. Estimates made 
by calorimetry from these data and from the potential value of 
the different foods give the total daily heat production as about 
2,500,000 calories for the average individual. This is equal to 
about 1,400 calories per hour per kilo weight. 

The English heat unit is the pound-degree F. It is the 
amount of heat necessary to raise i pound of water i degree F. 
Its mechanical equivalent is the force necessary to raise i pound 
772 feet. The estimates just given in the metric system when 
translated to English nomenclature give the total heat produc- 
tion for 24 hours as about 8,400 pound-degrees, or 2.5 per hour 
per pound weight. These figures are given as only approxi- 
mate and are subject to change by many causes, such as sex, 
cardiac and respiratory activity, internal and external temper- 
ature, exercise, digestion, age, nervous influences, the body 
weight, etc. 

Thermogenesis. — Thermogenesis, or the production of heat, 
is the result of activity on the part of tissues, nerves and cen- 
ters. Now, the potential energy of the foodstuffs is the ultimate 
source of all bodily heat no matter how it may be manifested, 
and it is evident from what has been said already that all the 
tissues of the body are heat-producing tissues, because oxidation 
processes go on in them all. But muscular tissue seems to be 
endowed with special heat-producing capabilities, so much so 
that it is said to generate heat as a specific product, and not as a 
mere incident of its metabolism. Muscle will reproduce heat 
when entirely at rest — when the nutritive metabolic changes are 
practically nil. The process seems to be regulated in accord- 
ance with the needs of the economy by means of a nervous 
mechanism, making the production of heat analogous to secre- 
tion. Separation of a muscle from its nerve does not stop 
thermogenesis, but markedly interferes with it in that part. The 



274 NUTRITION, DIETETICS AND ANIMAL HEAT. 

existence of distinct thermogenic nerves has not been demon- 
strated. The existence of specific thermogenic centers seems 
certain. Some of them increase and some decrease thermo- 
genesis. 

The general thermogenic centers are in the spinal cord. Cen- 
ters increasing thermogenesis are probably in the caudate nuclei 
of the corpora striata, the optic thalami, pons and medulla. 
Irritation of these regions causes a rise in temperature. The 
location of the thermo-inhibitory centers is a matter of specu- 
lation. The general thermogenic centers in the cord prob- 
ably maintain a fairly constant production of heat indepen- 
dently, but they are subservient to encephalic centers which 
excite them to increased or decreased activity by reason of 
certain impressions, cutaneous or otherwise, which they have 
received. 

Thermolysis. — About 85 per cent, of animal heat, discharged 
as such, is lost by radiation and evaporation from the skin; 
about 12 per cent, is dissipated in the lungs by evaporation and 
in warming the inspired air ; the remainder is discharged in the 
urine and feces (disregarding the small amount which goes to 
warm ingested articles). 

Heat is radiated from the body just as from a hot stove. Radia- 
tion is affected by the conductivity of the surrounding medium. 
For instance, in media of water and air of the same temperature 
the radiation is greater in water, because it -is a better conductor 
of heat. 

Evaporation from the skin is of very great importance in in- 
creasing heat dissipation. 582 calories of heat are consumed 
when one gram of water is vaporized ; and when this evaporation 
takes place on the skin the heat is abstracted largely from the 
body. This is said to represent nearly 15 per cent, of the total 
heat dissipation. Hence the value of perspiring in hot weather. 
Evaporation also takes place from the moist surfaces of the lungs, 
and, moreover, when, as is usually the case, the inspired air is 



THERM OTAXIS. * 275 

cooler than the lung structure a certain amount of heat is con- 
sumed in warming it. 

But it is not to be inferred that thermolysis takes place from 
the body just as from an inanimate object and that no "or- 
ganic ' ' process is involved. On the other hand, it is intimately 
connected with and influenced by circulation, respiration, secre- 
tion and other functions. When there is a tendency for the 
body temperature to rise, the circulation becomes more active 
and sends more blood to the periphery to be cooled ; respiration 
is augmented, causing a greater abstraction in the lungs ; the 
secretion of sweat, for instance, is increased. 

There may be distinct thermolytic centers. 

Conditions Influencing Heat Dissipation. — These have been 
suggested in a previous section. Heat dissipation is greater 
in proportion to weight in small than in large animals because 
the radiating surface is relatively larger. It is less in the female 
than in the male because she has, as a rule, a larger proportion 
of subcutaneous fat, which is a poor conductor of heat. It is less 
when the body is covered with clothing which is a poor con- 
ductor of heat than when the covering conducts heat readily. 
It is increased when the internal temperature is raised and when 
the external temperature is lowered. Any general increase 
in vascular or respiratory activity increases heat dissipation for 
reasons already given. When the external temperature is high 
and the air is dry evaporation is more abundant, and conse- 
qently heat dissipation is greater than when the air is already 
impregnated with moisture. Hence the oppressiveness of a 
high external temperature with high humidity. In fever heat 
dissipation is usually increased, but to a less degree than heat 
production. 

Thermotaxis. — Thermotaxis is the regulation of heat produc- 
tion and heat dissipation so that the temperature of the body 
may remain the same. It is evident that there is frequently a 
transient increase or decrease of thermogenetic activity • unless 



276 NUTRITION, DIETETICS AND ANIMAL HEAT. 

there be a corresponding change in therm oly tic activity the tem- 
perature will be disturbed. 

The temperature of the body is not necessarily raised when 
thermogenesis is increased, or lowered when thermogenesis is 
decreased ; for thermolysis may be, and in health is, correspond- 
ingly increased or diminished. Conversely, a change in ther- 
molysis does not necessarily mean an opposite change in the 
body temperature. Alterations which do occur in the temper- 
ature are the result of the improper regulation of the heat at 
hand. For instance, fever may result from average thermo- 
genesis and deficient thermolysis ; from increased thermogenesis 
and thermolysis when the latter is increased less than the former ; 
from diminished thermogenesis and thermolysis when the latter 
is diminished less than the former, etc. A subnormal tempera- 
ture is caused by opposite conditions. The temperature remains 
constant when thermogenesis and thermolysis are normal, or 
when they are increased or decreased correspondingly. 

Thermotactic activity is the result of changes in the tempera- 
ture of the blood, or of cutaneous impressions. A rise in the tem- 
perature of the blood excites thermolysis, as indicated. A cold 
atmosphere increases thermolysis, but at the same time it makes 
impressions on the cutaneous nerves which, when carried to the 
centers, excite thermogenesis and thus compensation is estab- 
lished. A cold bath lowers the temperature because thermolysis 
is increased more than thermogenesis. There is increased radi- 
ation because of the relatively increased difference in the tem- 
perature of the body and of the surrounding medium. On the 
other hand, the cold contracts the capillaries, diminishing the 
amount of blood exposed to the cooling influence of the water 
and decreasing the amount of sweat ; but these influences tend- 
ing to inhibit thermolysis are not equal to those augmenting it. 
However, in health, thermotaxis prevents the disturbance of the 
balance between thermogenesis and thermolysis to any great ex- 
tent, and the temperature cannot be lowered very much. These 



THERMOTAXIS. 277 

are only examples of the reciprocal relations maintained between 
the production and dissipation of heat, a disturbance of which 
relations is prevented under normal conditions by thermotaxis. 
Any change in one process is followed at once by a compensa- 
tory change in the other. 



CHAPTER IX. 
THE NERVOUS SYSTEM. 



General Functions of the System as a Whole. — The nervous 
system is the most delicately organized part of the animal 
body. Its sensory terminations receive impressions which 
are conducted to the centers ; it conveys impulses from the 
centers to the different parts of the body, controlling and 
regulating their action. Connecting, as it does, all parts of 
the organism into a coordinate whole, it is the only medium 
through which impressions are received, and is the only agency 
through which are regulated movement, secretion, calorification 
and all the processes of organic life. This system, ramified 
throughout the body, connected with and passing between its 
various organs, serves them as a bond of union with each other, 
as well as with the brain. The mind influences the corporeal 
organs through the instrumentality of this system, as when 
volition calls them into action ; on the other hand, changes in 
the organs of the body may affect the mind through the same 
channel, as when, for instance, pain is mentally perceived when 
the finger is burned. Thus it is that the nervous system becomes 
the main agent in what is known as the " life of relation " ; for 
without some medium for the transmission of its mandates, or 
some means of receiving those impressions which external objects 
are capable of exciting, the mind would be completely isolated, 
and could hold no communion with the external world. 

It should not be understood, however, that the nervous system 
cannot operate independently of mental influence. All those 
manifestations of nervous activity connected with the perform - 

278 



GENERAL FUNCTIONS. 279 

ance of the so-called " organic functions" of life, as digestion, 
circulation, etc., are not directly influenced by volition ; indeed 
an essential character of these functions is that they are com- 
pletely removed from the influence of the will ; to be conscious 
subjectively of their performance is an evidence of abnormality. 

The first step in every voluntary act is a mental change, in 
which the act of volition consists. If this mental change be of 
such nature as to direct its influence upon a muscle, or a particular 
set of muscles, the contraction of those muscles immediately 
supervenes, so as to bring about the predetermined voluntary act. 
But the influence of the will could not possibly be exerted upon 
those muscles except through intervention of the nerves. 

Furthermore, a certain mental state, in cases of common or 
special sensation, is induced by an impression made upon certain 
bodily organs. But in no case could the mental state be pro- 
duced unless a particular part of the nervous system were present 
to convey the impression received to the center capable of rec- 
ognizing it. If the hand be burned pain is felt, but were the 
nerves not present to convey the impression made by the heat 
no degree of temperature could make the mind cognizant of 
injury. When light is admitted to the eye a corresponding 
mental sensation is produced, but for the production of this the 
integrity of the optic nerve is a necessary condition. 

It will be gathered from the foregoing remarks that the nerv" 
ous system is not only capable of conveying communications, 
but that it has the power, in certain of its divisions, of receiving 
impressions and of giving rise to stimulating influences — that is, 
that it is capable of generating a peculiar power known as 
" nerve force" It thus becomes the seat of distribution of en- 
ergy to all the cells. These generating parts of the system are 
the reservoirs of force — force which has been derived from the 
cells and is distributed to them. This nervous force, having its 
origin in the living activity of the cells, is the highest manifesta- 
tion of vital energy. 



280 THE NERVOUS SYSTEM. 

The nervous structure is divided into two great systems ; 

i. The Cerebro-Spinal System consists of the brain, the 
spinal cord and all the nerves which run off from these. This 
system is especially concerned with the functions of relation, or 
of animal life. It presides over general and special sensation, 
over voluntary movements, over intellection, over all conscious 
activity, and over all other functions which are peculiar to the 
animal. It is by this system that we know of and deal with the 
other great system. It is also called the Animal, or Inorganic, 
System. 

2. The Sympathetic, Organic, Ganglionic or Vegetative 
System is especially connected with the functions relating to 
nutrition — functions similar to those occurring in the vegetable 
kingdom. It presides over all organic life — over all uncon- 
scious activity. While the operations over which this system 
holds sway are quite different from those under the supervision 
of the cerebro-spinal system, it must not be concluded that 
the two are not anatomically and physiologically related. 
Neither is independent of the other, as was once thought, but 
both are parts of the same great apparatus. 

Divisions of the Nervous Substance as a Whole. — The 
nervous matter, irrespective of the two systems, may be studied 
as consisting of two divisions. The first is made up of cells ; 
the second of tubes, or fibers. Although the tissue may be thus 
divided into nerve cells and nerve fibers, the present conception 
of the arrangement of the nervous substance is that these two 
are only different parts of the same element known as the neuron, 
supported by tissue elements known as neuroglia, which, though 
not identical with connective tissue, is comparable to it in its 
function of support. The neuron, thus considered, consists of a 
protoplasmic body which sends out a number of branching proc- 
esses called dendrites, one of which becomes the axis cylinder. 
While, therefore, it is to be understood that the cell and the fiber 
in the nervous system are both portions of an identical whole, a 



NERVE FIBERS. 251 

description of them as separate parts is warranted for the sake of 
convenience and by differences in their general characteristics. 

The nerve cells are the only organs capable, under any cir- 
cumstances, of generating nerve force. As a rule they are stimu- 
lated to generate this force by the reception of an impression 
through the nerve fiber, but they may in some cases be directly 
excited by mechanical, electrical or chemical means. They 
also frequently act as conductors, as will be seen later. 

Under no circumstances can nerve fibers generate force. 
Their office is exclusively to conduct impressions and impulses, 
and they usually receive these impressions and impulses at their 
terminal extremities in the case of afferent nerves, and from the 
centers in the case of efferent nerves ; but in many instances 
they may be stimulated in any part of their course. Some fibers 
are incapable of being thus directly stimulated. The nerves of 
special sense are insensible to direct stimulation. 

Nerve Fibers. — Nerve fibers are of two kinds : (A) white or 
medullated fibers and (i?) gray or non-medullated fibers. The 
non-medullated fibers possess the conducting element alone, 
while the medullated possess certain accessory anatomical ele- 
ments. 

(A) Each medullated fiber has (i) an external enveloping 
membrane called the neurilemma, or the primitive nerve sheath, 
or the sheath of Schwann ; (2) an intermediate substance known 
as the myeline sheath, or the white substance of Schwann, or the 
medullary substa7ice ; ( 3 ) a central fiber, the true conducting 
element, which usually goes under the name of the axis cylinder, 
or axione. 

The sheath of Schwann is analogous to the sarcolemma of 
muscle fibers. It is a structureless protective membrane, some- 
what elastic, and presents oval nuclei with their long diameter 
corresponding to the direction of the fiber. This sheath is 
wanting over the medullated fibers in the white substance of the 
brain and spinal cord. 



282 



THE NERVOUS SYSTEM. 



Fig. 59. 



Node of Ranvier. 



Primitive sheath. 



Nerve corpuscles. 



Axis cylinder. 



White substance 
of Schwann. 



Node of Ranvier. 



Scheme of a Medullated 
Nerve-Fiber of a Rab- 
bit Acted on by 
Osmic Acid. 

The incisures are omitted. > 
400. (Landois.) 



It is the white substance of Schwann 
which gives to the nerve its peculiar 
whitish appearance. This is a fatty 
substance of a semi-fluid consistence. 
It fills the tube made by the sheath of 
Schwann and surrounds the axis cylin- 
der. It is wanting at the origin of the 
fibers in the centers and at their periph- 
eral distribution. It is probably not 
necessary to conductivity. In fresh 
nerves this substance is strongly refrac- 
tive, and the optical effect produced by 
its varying thickness in the center and 
at the edges is the appearance of dark 
borders. It easily coagulates into an 
opaque mass. The idea that the mye- 
line sheath acts as an insulator lacks 
supporting evidence. The theory that 
it is nutritional is plausible ; but no suf- 
ficient difference in the medullated and 
non-medullated fibers in this respect 
has been found to establish the theory 
as a fact. At certain points in the 
course of medullated fibers there are 
seen constrictions called the nodes of 
Ranvier. At these points the medul- 
lary substance is wanting and the sheath 
of Schwann is in contact with the axis 
cylinder. It is not improbable that 
these nodes furnish a mode of access for 
the nutrient plasma. Certain it is that 
they are most numerous where physio- 
logical activity is supposed to be most 
active. 



NERVE FIBERS. 



283 



Fig. 60. 



The axis cylinder is composed of a large number of primitive 
fibrillar. This band occupies about one- 
fourth the diameter of the tube and is 
the true conducting element, as is shown 
by its invariable presence, its continuity 
and other considerations equally con- 
clusive. It is demonstrated under the 
microscope with difficulty in fresh speci- 
mens. It is directly connected with a 
nerve cell, and is the essential part of 
the fiber. The process of the cell which 
becomes the axis cylinder is not, as was 
once thought, unbranched, but itself 
sends off " collaterals " in the gray sub- 
stance. These collaterals, however, do 
not actually join any other nerve cell 
or fiber. 

The average diameter of medullated 
fibers is about ^-qVq in -> though all are 
said not to preserve the same diameter 
throughout their course. 

(£) The non-medullated fibers (fib- 
ers of Remak) seem to be simple axis 
cylinders without the other anatomical 
elements peculiar to medullated fibers. 
They make up a large part of the trunks 
and branches of the sympathetic sys- 
tem, and represent the filaments of 
origin and distribution of all nerves. 
They are thought by some to possess a 
neurilemma. They are pale gray in 
color. 

Nerve Trunks. — The above remarks 
apply to a single nerve fiber. These 




Xon-Medullated Nerve- 
Fiber. 

Vagus of dog. b, fibrils ; u, 
nucleus ; fi, protoplasm sur- 
rounding it. {Stirling.) 



284 



THE NERVOUS SYSTEM. 



fibers seldom run an extended course alone, but are bound 
together in large numbers to make a nerve trunk. This 
trunk is composed of a number of bundles of libers, and is sur- 
rounded by a connective tissue membrane known as the epineu- 
rium ; the separate bundles, or funiculi, are surrounded each by 
a similar membrane called the perineurium ; while inside the 
funiculi, between the primitive fasciculi, is a delicate supporting 

Fig. 61. 




Transverse Section of a Nerve. (Median.) 
efi, epinerium ; fie, perinerium ; ed, endonerium. {Landois.) 

tissue known as the endoneurium, or the sheath of Henle. In con- 
nection with this sheath there are nuclei belonging to the con- 
nective tissue and to the nerve fibers themselves. The sheath be- 
gins where the nerve fibers emerge from the white portion of the 
centers, is interrupted by the ganglia in the course of the fibers, 
branches as the bundle branches, and is lost before the terminal 
distribution is reached. It is seldom found surrounding single 
fibers. It is likewise rare for capillaries to penetrate it and reach 



NERVE CENTERS. -285 

the fibers themselves. There are numerous lymph spaces around 
the individual fibers as well as around the funiculi. In situations 
where the nerves are well protected, as in the cranium, the amount 
of fibrous tissue in the trunks is small, but where opposite condi- 
tions prevail, as in muscular substance, this tissue is largely in- 
creased in amount as regards both that which surrounds the 
trunk and that which is sent in between the funiculi and fibers. 
This tissue has ramifying in it a network of fibers known as 
nervi nervorum. The blood supply is not large. 

Individuality of Nerve Fibers. — It is to be remembered that 
so far as can be determined every nerve fiber, having entered a 
trunk, proceeds without interruption ,to the part to which it is 
finally distributed, whether that part be the skin, or a viscus, or 
a muscle, or a gland, or some organ of special sense, or another 
nerve cell, or what not. Collections of fibers forming bundles 
run together in the same trunk, may leave that trunk together, 
may send out part of their fibers to another bundle or trunk, or 
may receive other fibers from other funiculi ; but everywhere the 
relation of the primitive fibers to each other is simply one of 
contiguity. However, as the axis cylinder approaches the seat 
of its final distribution, it breaks up into several fibrillae, such 
divisions always taking place at the nodes of Ranvier. 

Nerve Centers. — The nerve centers include the gray matter 
of the brain and cord and the ganglia in both the cerebro-spinal 
and sympathetic systems. These centers have a gray color due 
to the presence of a pigmentary substance in the cells and sur- 
rounding tissue. The ganglionic centers are simple collections 
of nerve cells with their usual accessory elements — myelocytes, 
intercellular granular matter, delicate membranes covering some 
of the cells, connective tissue elements, blood-vessels and lym- 
phatics. 

Nerve Cells. — These are irregular in shape and may be uni- 
polar, bipolar or multipolar. They also vary much in size. The 
unipolar cell has a single prolongation which becomes the axis 



286 



THE NERVOUS SYSTEM. 



cylinder. Bipolar cells are prolonged in two directions, and may 
be looked upon as simply protoplasmic enlargements of the nerve 
fiber. This cell is frequently covered by a connective tissue en- 
velope which is continuous in both directions with the sheath of 
Schwann. Multipolar cells have three or more prolongations, 
one of which always becomes continuous with the axis cylinder 
and is called the axis-cylinder process, the neuraxon, or the axione. 

Fig. 62. 



Nerve process 
or axione. 

Neurilemma. 



Neurilemma. 




, Nerve-cell. 



A B 

A, efferent neuron ; B, afferent neuron. (Brubaker.) 

The other poles branch in various irregular directions like the 
limbs of a tree, and are hence called dendrites. They also go 
under the name of protoplasmic prolongations. Some of these 
unite the cells to contiguous cells by interlacing with, but not 



NEURONS. -287 

actually joining, similar poles from those cells. The multipolar 
cells in the anterior cornua of gray matter of the cord are said 
to be larger in size and to present more poles than corresponding 
cells in the posterior columns. 

The diameter of nerve cells varies from 12 1 50 to z ^ in. The 
nucleus is usually single, and most cells have no true surrounding 
membrane. If a nerve fiber be followed toward the center 
which gives it origin it will be found first to lose its sheath and 
later its medullary substance ; this medullary substance may con- 
tinue for some distance after the sheath is lost, as in the white 
substance of the encephalon, but never penetrates the gray sub- 
stance proper. Every nerve fiber is connected with a cell by 
that cell's axis-cylinder prolongation. 

Certain retrograde changes take place in the neurons in old 
age — morphological changes agreeing with the physiological de- 
crease in energy-producing power at that time. The cell body 
becomes smaller, the dendrites atrophy, and the axiones diminish 
in mass. Nerve " fatigue " can also be demonstrated by the 
microscope. The nuclei of the sheath are flattened, the proto- 
plasm is shrunken and vacuolated and the nucleus is crenated. 
The quantity and quality of the food may be perfect, but the 
power of the cell to utilize it is impaired, and this means dimin- 
ished physiological power. 

Communication Between Different Neurons. — Every neuron 
is a7iato?7iically independent of every other neuron. There is no 
actual joining of fibers or dendrites — simply an interlacement of 
the end arborizations. This is illustrated in Figs. 63 and 64. 
In the latter the afferent fiber is joined to no cell except G, one 
of the cells of the spinal root ganglion. Its end arborizations 
simply interlace with the dendrites of the motor cell M. C. and 
cause it to send out an efferent impulse to the muscle M. 

Furthermore, there are frequent relays in the transmission of 
nerve messages. By no means do all the fibers from the motor 
area of the brain pass themselves out as parts of the anterior roots. 



M.C 




Reflex Action: Old Idea. (K/r/ces.) 

Fig. 64. 




Reflex Action: Modern Idea. {Kirkes.) 



Fig. 65. 




S.C. 




L. 
S. 




M 



Diagram of an Element 
of the Motor Path. 
U.S, upper segment ; L. 
S. lower segment; C.C, cell 
of cerebral cortex; S.C, cell 
of spinal cord, in anterior 
cornu ; M, the muscle; S, 
path from sensory nerve roots. 
(Kirkes after Gozuers.) 
x 9 



NERVE FIBERS. 2#g 

The relay service is illustrated in Fig. 65. 
Here again, it is seen that there is no actual 
joining of the neurons. Whenever it is said 
that a nerve cell is "joined" to another, or 
that the axis cylinder of a cell "joins" 
another cell, no actual continuity of tissue 
is meant. Different neurons communicate 
only by contiguity. 

Peripheral Nerve Terminations. — 
Nerves terminate peripherally ( 1 ) in 
muscles, (2) in glands, (3) in special or- 
gans connected with the senses of sight, 
hearing, smell and taste, ( 4 ) in hair- 
follicles, (5) in simple free extremities 
passing between epithelial and other cells, 
and (6) in several kinds of so-called tactile 
corpuscles. 

The motor nerves passing to voluntary 
muscles form first a ' ' ground plexus ' ' for 
each group of muscle bundles — this plexus 
being made of the axis-cylinder fibrillar. 
From this plexus fibrils pass to form an 
' i intermediary plexus ' ' corresponding to 
each muscle bundle. These fibrils are still 
meduilated, and when a branch from the 
intermediary plexus enters a muscle fiber 
its sheath becomes continuous with the 
sarcolemma of that fiber, and the axis- 
cylinder fibrils form a network on the sur- 
face of the muscle fiber. This is called an 
end motorial plate. It contains a number 
of nuclei, and sends off from its under sur- 
face fine nbrillae which are said to pass 
between the muscular fibrillae which make 



290 



THE NERVOUS SYSTEM. 



up the fiber. Sensory fibers are somewhat scantily distributed 
to the voluntary muscles. 

In plain muscle tissue the motor nerves are distributed after 
the same general manner as in the striped muscles, though with 
some differences. Here the fibers are not medullated, and 

Fig. 66. 




End-plate. 



Muscle nucleus. 



Nerve-fibre. 

Termination of a Nerve-Fiber in End-Plate of a Lizard's Muscle. {Stirling.) 

primitive fibrils passing from the intermediary plexus finally 
enter the nuclei of the muscle cells. 

Medullated fibers have been traced to the cells of glands, 
but not farther. It is thought by some that, having formed a 
plexus, non-medullated fibers pass in to terminate in the nu- 
cleoli of the gland cells, though such endings have not been 
demonstrated. 

The peripheral distribution of nerves connected with the 
special senses will be discussed elsewhere. 

The remaining methods of termination above noted apply to 
afferent nerves. It is claimed that a very large number of sen- 
sory nerves terminate in hair-follicles. If such be the case it 
will account for sensory terminations in by far the greater part 
of the cutaneous surface. It is supposed that nerve fibrillar form 
a plexus beneath the true skin and send branches thence to the 



NERVE FIBERS. 



•291 



Fig. 67. 



follicles, though the exact mode of termination is a question of 
some obscurity. 

Terminations between epithelial cells are probably more com- 
mon than any other method of sensory distribution. The fibers, 
having passed to the surface of the 
skin or mucous membrane, lose 
everything excepting the axis- 
cylinder, which, dividing into 
minute ramifications, passes, by 
means of these fibrillar, among the 
epithelial cells. This mode of 
termination is held by some to 
prevail in the glands. It certainly 
prevails in parts other than the 
skin and mucous membranes. 

Sensory nerves further terminate 
in (a) the corpuscles of Paci?n or 
Vater, (b) the end bulbs, or tactile 
corpuscles, of Krause^c) the tactile 
corpuscles of Meissner, (a 7 ) the 
tactile menisques, and (<?) the cor- 
puscles of Golgi. 

(a) The Pacinian corpuscles 
are oval elongated bodies. Each 
corpuscular body has a length of 
about y 1 ^- of an inch, and is about 
half as broad. It is made up of a 
number of concentric layers of 
connective tissue in a hyaline 
ground substance, and is attached 
by a pedicle to the nerve whose 

termination it is. Through this Vater's or Pacini's Corpuscle. 

pedicle passes a Single (Occasion- a > stalk; f> nerve-fiber entering it; c,d, 

connective-tissue envelope; e, axis-cylin- 

ally more) nerve fiber which, der with its end divided at /: {Landois.) 




292 



THE NERVOUS SYSTEM. 



Fig. 68. 



piercing the several concentric layers constituting the cor- 
puscle, gradually loses its myeline substance and runs longi- 
tudinally through the center of the body to terminate at the 
distal end of the central cavity in a knob-like enlargement. 
These corpuscles are found in great abundance on the palmar 
and plantar surfaces of the hands and feet, being far more 
numerous on the first phalanx of the index finger than elsewhere. 
About six hundred are said to be present in each hand and foot. 
They are also to be found on the dorsal surfaces of the hands 
and feet, over parts of the forearm, arm and neck, in the nipples, 
in the substance of muscles, in all the great plexuses of the sym- 
pathetic system, and in numerous 
other situations. These bodies can- 
not be considered true tactile cor- 
puscles because they are situated be- 
neath the skin ; neither can they be 
positively said to have any " special 
sensory" function, such as the ap- 
preciation of temperature, weight, 
etc. 

(£) The end bulbs of Krause 
exist in great number in the con- 
junctiva, the glans penis and clitoris, 
the lips, and in other situations. 
They bear some resemblance to the 
corpuscles of Pacini, but are much less elaborate in their arrange- 
ment ; the number of concentric layers is much smaller, while the 
contained mass is larger. The shape is spherical. From one to 
three medullated fibers pass from the underlying plexus to w T ind 
through the corpuscle and break up in free extremities. The 
sheath of the fiber is continuous with the outer covering of the 
corpuscle, and the medulla is gradually lost as the fiber enters 
the bulb. The end bulb of Krause measures from T -oVo to 
of an inch in diameter. 




End Bulb from Human Conjunc- 
tiva, Treated with Osmic Acid, 
Showing Cells of Core. (From 

Yeo after Longworth.) 
a, nerve fiber ; b, nucleus of sheath ; 
c, nerve fiber within core ; d, cells of 
core. 



1 

5 



NERVE FIBERS. 



. 2 93 



(c) The tactile corpuscles of Meissner have to do with the 
sense of touch, and are situated largely in the- papillae of the 
skin covering the palmar surfaces of the hands and the plantar 
surfaces of the feet ; they also exist in other situations, corre- 
sponding in general to the distribution of the Pacinian corpus- 
cles. The largest number is found over the distal phalanges of 
the fingers and toes on their palmar and plantar surfaces ; they 

Fig. 69. 




Drawing from a Section of Injected Skin. 
Showing three papillae, the central one containing a tactile corpuscle, a, which is con- 
nected with a medullated nerve, and those at each side are occupied by vessels. (From Yeo 
after Cadiat.) 

diminish in number proximally from these points. They may 
be simple or compound according as the enclosing capsule con- 
tains one or more collections of nucleated cells. Their form is 
oblong with the long axis in the direction of the papilla. They 
vary in thickness with the papillae of the region in which they 
are located. They may have a transverse diameter of from 
siro to Tiro °f an i ncn ? an d probably in most instances occupy 
the secondary eminences of the papillae in which they are found. 
A simple papilla does not generally possess both vascular and 
nervous loops. 

(d) The tactile menisques are found in certain cutaneous re- 
gions. Nerves in the superficial layer of the skin lose their 
medullary substance and divide to form arborizations which are 
flattened into the form of a leaf. 



294 THE NERVOUS SYSTEM. 

(e) The corpuscles of Golgi are situated at the point of union 
of tendons with muscles, and are believed by some to have to do 
with the muscular sense. They are flattened fusiform bodies 
composed of granular substance enclosed in layers of hyaline 
membrane and containing nervous fibrillar. 

Properties and Classification of Nerve Fibers. — Nerve fibers 
are for the purpose of conveying messages either peripherally or 
centrally. They may be stimulated to action by anything 
capable of suddenly increasing their irritability. In any case 
the effect of the stimulus, whether normal or abnormal, is mani- 
fested at the peripheral distribution of the stimulated fiber. So 
far as most external manifestations are concerned, nerves may 
be classified as motor and sensory. That is to say, stimulation, 
for instance, of a cerebro-spinal nerve (except those of special 
sense) is followed, under ordinary conditions, by one of two re- 
sults — there is either pain or contraction of a muscle to which 
the nerve is distributed. This is a typical illustration of the 
action of motor and sensory fibers, and the manifestation of nerve 
action, whether it consist in pain or motion, is a result only of 
the conduction of an impression or an impulse to the center or 
the periphery. It is to be noted that the result of thus stimu- 
lating a nerve fiber is manifested at one extremity only of that 
fiber, and always at the same extremity. 

However, since there are nerve fibers the stimulation of which 
is not followed by pain or motion, the division into sensory and 
motor fibers is not comprehensive enough to include all the 
fibers in the body. But since, as above stated, the only office 
of fibers is to conduct, and since they always conduct in a direc- 
tion either toward or away from the center, all nerves may be 
classified as either centripetal or centrifugal. A corresponding 
division is into afferent and efferent. It will be seen that all 
motor fibers are centrifugal or efferent, but not all centrifugal or 
efferent fibers are motor. It will likewise be seen that all sen- 
sory fibers are centripetal or afferent, but not all centripetal or 



EFFERENT NERVES. 2 95 

afferent fibers are sensory. For impressions made upon the 
terminations, or upon the trunk, of a centripetal nerve may cause 
(1) pain f or some other kind of sensation \ (2) special sensa- 
tion ; (3) reflex actio m of some kind; (4) inhibition. Similarly 
impressions made upon a centrifugal nerve may (1) cause con- 
traction of a muscle (motor nerve) ; (2) influence nutritio?i 
(trophic nerve) ; (3) control secretion (secretory nerve) \ (4) 
inhibit, augment, or 3 top any other efferent action (Kirkes). 

To these two classes, efferent and afferent, should be added a 
third, the intercentral fibers which connect different parts of the 
nervous centers. Most of these even can be called either afferent 
or efferent. 

Characteristics of Efferent Nerves. — In case of these nerves 
a force is generated in the centers and conveyed by the nerves 
to the periphery, where it manifests itself in one of the ways 
mentioned above as characteristic of centrifugal fibers. Division 
of these fibers, or interference with their conductivity by disease 
or otherwise, renders impossible the manifestation of nervous 
force generated in the center, for the simple reason that the organ 
to which the fibers are distributed cannot receive the message 
intended for it. For instance, a muscle cannot, by the most per- 
sistent effort of the will, be made to contract if the motor fibers 
running to that muscle are divided. In case, however, of divi- 
sion of efferent nerves, if the peripheral end be irritated, thus 
roughly counterfeiting normal stimulation, the ordinary effects 
of normal stimulation will be brought about, provided (as is 
usually the case) that particular nerve can be thus directly stimu- 
lated. Stimulation, however, of the central end of such a cut 
nerve produces no effect. No matter whether such efferent 
nerves receive their stimulus directly from the center or artifi- 
ficially, as by mechanical or electrical means, the effect is pro- 
duced in the end organs, whatever they may be. It is an in- 
variable law, to which reference has already been made, that a 
nerve fiber thus conducting a message in either direction is not 



296 THE NERVOUS SYSTEM. 

interfered with by the proximity of other fibers, similar or dis- 
similar. Such message is not in any way imparted to a neigh- 
boring fiber or diffused through the fasciculus, but is conveyed 
uninterruptedly to its destination. It is possible that the mye- 
line sheath has an insulating effect upon the contained axis 
cylinder, just as an electric wire may be insulated by non-con- 
ducting substances like silk, but this is doubtful. 

Interesting manifestations of motor centrifugal impulses are 
seen in certain movements associated with corresponding mus- 
cles on different sides of the body and with sets of muscles on the 
same side. It is almost impossible to effect certain movements 
with a single finger or toe without causing similar movements in 
other fingers and toes ; a part of a muscle cannot be made to 
contract separately ; it is doubtful if it be possible to move one 
eye-ball without the other, even by the most persistent practice. 
Other similar examples are numerous. It is quite probable that 
in most cases these associated movements are solely matters of 
habit. But the connection by commissural fibers of the cells in 
the centers controlling and regulating the movement of these 
muscles and sets of muscles would offer a not unreasonable ex- 
planation of the phenomena in question, since such an arrange- 
ment might render impossible separate and individual action by 
the cells thus connected. Excepting, perhaps, the movements 
of the eye-balls, these associated movements can be greatly 
modified by education. 

Characteristics of Afferent Nerves. — Impressions received by 
these fibers, although they are conveyed toward the center and 
must reach a center before there is any nervous manifestation, are 
always referred to the periphery. A most common illustration of 
this fact is furnished by injury to the ulnar nerve as it passes the 
elbow — such injury being manifested not usually by any pain at 
the point of infliction, but on the ulnar side of the hand where 
the nerve is distributed, A person whose limb has been ampu- 
tated often seems to feel pain in the extremity although it has 



AFFERENT NERVES. 297 

been removed from the body — such pain coming from compres- 
sion by the cicatrix (or otherwise) of the nerves which before 
the amputation were distributed to the severed limb. Here, as 
in the case of efferent nerves, division of the fibers between the 
seat of impression and the center precludes the possibility of 
any nervous manifestation. That is to say, no pain will be felt, 
no matter how great the injury be, if the sensory fibers running 
from the seat of injury be divided. Stimulation of the periph- 
eral end of a divided afferent fiber produces no effect \ but 
stimulation of the central end is followed by the ordinary mani- 
festation — by pain if the nerve stimulated be a common sensory 
one. This remark, of course, applies only to those nerves 
which can be thus directly stimulated — typically to true sensory 
fibers. 

Impressions conveyed by nerves of special sense must be re- 
ceived through the intervention of certain complex organs, con- 
sideration of which belongs elsewhere. 

Although a division has been made of nerve fibers into afferent 
and efferent, each with definite, proper and dissimilar functions 
so far as the direction of conduction is concerned, it has been 
impossible to discover any actual difference in the composition, 
appearance, or other properties, of the actual fibers themselves. 
In fact, it may be even considered as only an accident that one 
fiber conveys a message peripherally and another centrally — an 
accident dependent upon the kind of center with which the fiber 
is connected and the kind of termination it has in the periphery. 

Direction of the Current in Nerve Fibers. — It has long been 
understood that in no case will a fiber in situ convey a message at 
one time in one direction and at another in an opposite one, that 
no individual fiber can be both afferent and efferent \ and so far as 
practical action is concerned this is true, but "experiment has 
shown that if a nerve trunk be stimulated at a given point, then 
the nerve impulse can be demonstrated as passing away from the 
point of stimulation in both directions ' ' (American Text-book) . 



298 THE NERVOUS SYSTEM. 

However, only the message traveling in the physiological direction 
is manifest, for it is the only one which finds a suitable terminal. 

It is not to be concluded, however, that in any nerve trunk, as 
the ulnar nerve, there may not be both afferent and efferent 
fibers. Such, in fact, is the usual arrangement. Any nerve 
trunk may contain all kinds of fibers — sensory, special sensory, 
vasomotor, motor, trophic, secretory — but the presence of all 
these does not interfere with the individuality and the individual 
action of each fiber. A nerve trunk containing more than one 
kind of fibers is called a mixed nerve. 

Speed of Nervous Conduction. — It is stated that afferent im- 
pressions are conveyed by nerves at the rate of about 120 feet 
per second \ the rate for efferent impulses is somewhat less 
rapid, probably no feet. In the spinal cord tactile impressions 
are conveyed a little faster than in the nerves proper, and painful 
impressions somewhat less than one-half as fast. The rate of 
motor conduction in the cord is said to be one-third the rate in 
the nerves. It has also been demonstrated that an act of volition 
requires a definite time for the inception of its performance ; this 
is stated to be about Jg- of a second. The recognition of a 
simple impression (conveyed in the opposite direction, of course) 
requires about -^ of a second. Furthermore, the part played by 
the spinal cord in reflex action (to be considered later) also con- 
sumes an appreciable period • this is found to be more than 
twelve times the period occupied in the transmission of the im- 
pression to the cord or the impulse back to the muscles. 

Action of Electricity Upon Nerves. — A nerve may be irri- 
tated in any one of several ways \ but mechanical, thermal and 
chemical irritants, besides working injury to the tissues, are 
much less easily managed and regulated than is electricity. 
This agent may be applied time after time to a nerve trunk 
without causing any permanent change in its conductivity, and 
the strength, time and duration of application, etc., can be accu- 
rately governed. 



ELECTRICAL STIMULATION. 299 

In physiology and in therapeutics two kinds of currents are 
made use of — the primary or galvanic, and the induced or 
faradic. The simplest galvanic cell consists of two plates, one 
of zinc and the other of copper, immersed in properly acid- 
ulated water. Various complex modifications of this cell have 
been introduced, and they add to the convenience or efficacy of 
the current ; but the principle of all is the same. When these 
two pieces of metal, thus immersed, are united by a wire, what 
we call an electric current flows from the zinc to the copper 
through the immersing fluid, and from the copper to the zinc 
through the wire. Several of these cells properly united add to 
the force of the current, and they are generally so united for 
practical use. Since the current flows from the copper to the 
zinc through the connecting wire, the end of the wire connected 
with the copper is called the positive pole, or anode, and the end 
connected with the zinc the negative pole, or kathode. If now, 
one of these wires be brought in contact with a motor nerve no 
result is ordinarily seen, but at the moment when the other one 
also touches the nerve a single quick twitching of the muscle 
occurs. The moist tissue of the nerve (being a conductor) has 
completed the circuit, and the current of electricity flows through 
that nerve, having a direction, of course, from the anode to the 
kathode. The effect of this sudden flow of the electric current 
through the nerve is to stimulate it, and the muscle to which it 
is distributed contracts. Instead of the simple ends of the 
wires, electrodes with insulated handles are more conveniently 
employed. 

When the ends of the wires connected with the two plates are 
brought in contact with each other, or with any other substance 
which is a conductor of electricity, the current is allowed to flow 
through in the usual manner. The act of making such connec- 
tion is termed making, or closing, the circuit ; the act of breaking 
such a connection is termed breaking, or opening, the circuit. 

The induced, or faradic, current is developed by partially or 



300 THE NERVOUS SYSTEM. 

completely surrounding, with a coil of comparatively large wire, 
a similar coil of smaller wire through which a primary current is 
passing. At the exact moment of closure of the primary cur- 
rent in this case an instantaneous current of electricity is devel- 
oped in the coil of large wire (induction coil). The induced 
current is only momentary in duration \ it does not continue 
while the primary current remains closed. However, when the 
primary current is broken a second current is induced in the sur- 
rounding coil. This is likewise instantaneous in duration. It 
is to be observed that in the induction coil the first (making) 
current is in the opposite direction to that in the primary coil, 
while the second (breaking) current is in the same direction. 
It will be seen later that in the primary current the making shock 
is more vigorous than the breaking shock ; with the induced cur- 
rent the reverse is true. The primary current is a constant one, 
and, although ordinarily a twitching of the muscle to which a 
nerve is distributed is noticed both on making and breaking the 
circuit through that nerve, no disturbance of the muscle is noticed 
between the time of making and breaking. 

Conditions Affecting Electrical Stimulation of Nerves. — The 
effects of the stimulation of a nerve by an electric current de- 
pend upon the following considerations : ( i ) The rate at which 
the intensity changes ; (2) the strength, (3) density and (4) di- 
rection of the current ; (5) the duration and (6) angle of its ap- 
plication. 

1. It has been found that nerves subjected to the passage of an 
electric current of considerable strength have produced in them 
no change which will bring about muscular contraction provided 
that current be- very weak when begun and increase very grad- 
ually in strength. When the current is as gradually withdrawn 
there is no contraction. The natural conclusion is that it is not 
the strength of the current, but the suddenness of its introduction 
and withdrawal which accounts for the shock. Instruments in- 
tended to suddenly increase or diminish the strength of currents 



ELECTRICAL STIMULATION. 30I 

already passing through nerves have been devised, and the effect 
of their manipulation is the same as if new currents were intro- 
duced and withdrawn. 

With regard to the stimulating effects of making and breaking 
the current, it has already been said that the making shock in 
the direct current is stronger than the breaking shock. The 
making contraction has its origin at the kathode, and the breaking 
contraction at the anode. That is to say, the irritation process 
which manifests itself by muscular contraction begins and dif- 
fuses itself through the nerve from the kathode when the current 
is made, and from the anode when "* the current is broken. It 
has been actually found that the time elapsing between the intro- 
duction of the current into the nerve and the muscular contrac- 
tion is longer on making the current when the kathode is the 
more distant from the muscle, and longer on breaking the circuit 
when the anode occupies a similar relative position. The ex- 
citatory process at the two poles is different, being of such nature 
at the kathode as to bring about contraction on closing, and at 
the anode as to produce a similar effect on opening. 

Furthermore, closing contractions are stronger than opening 
contractions. The irritation produced at the kathode is stronger 
than that produced at the anode. Suppose experimentation be 
begun with a very weak current. It will be found at first that 
contraction follows closure of the current only, and that these 
contractions gradually increase in strength as the current in- 
creases. Soon, however, slight contractions are noticed on 
opening, and these also gradually increase in strength with the 
current, but are persistently less vigorous than the correspond- 
ing closing contractions. This relation is found to be disturbed 
later by further increasing the strength of the current and by 
varying its direction. 

2. In estimating the effect of the strength of a current it is 
customary to use the induction coil, since its intensity can be 
more easily regulated. Here the making contraction is weaker 



3° 2 



THE NERVOUS SYSTEM. 



than the breaking contraction — the opposite of the conditions 
existing in connection with the primary current. The general 
rule is that the irritation increases with the strength of the current, 
though in case of very strong currents the results may be affected 
by changes in the irritability and conductivity of the nerves. 

3. Given a fixed current and a conductor of varying diameter, 
the density of the current will be greatest where the diameter of 
the conductor is least ; and here it is that the irritating effect of 
the current is greatest. 

4. It has been discovered that the effect of electrical stim- 
ulation of a nerve depends upon the direction of the current in 
the nerve. The current through the nerve is from the anode to 
the kathode, and this current is descending or ascending accord- 
ing as the anode is the farther from or the nearer to the muscle. 
With a • current of weak strength there is contraction only on 
closing for both descending and ascending currents. With a 
medium current there is contraction on both closing and opening 
for currents in either direction. With a strong current there is 
contraction only on closing for the descending current, and only 
on opening for the ascending current. The following table in- 
dicates Pfliiger's Lazu of Contraction : 



Strength of Current Used. 


Descending Current. 


Ascending Current. 


Make. 


Break. 


Make. 


Break. 


Weak 

Moderate 

Strong 


Yes. 
Yes. 

Yes. 


No. 
Yes. 

No. 


Yes. 
Yes. 

No. 


No. 
Yes. 

Yes. 



Remembering that the irritation developed at the kathode is 
stronger than that developed at the anode, and that the irritation 
responsible for the contraction is at the kathode when the cur- 
rent is closed and at the anode when it is opened, the phe- 
nomena accompanying the passage of the strong current are the 
only ones difficult of explanation. It is possible to explain them 



ELECTRICAL STIMULATION. 303 

as follows : When a strong current is made to pass through a 
nerve the conductivity of that part of the nerve to which the 
anode is applied is so materially diminished that it may consti- 
tute a block to the passage of the stimulus. Moreover, at the 
moment of opening the current the power of conductivity is 
suddenly restored in the region of the anode, and markedly 
diminished, or lost, in the region of the kathode. In descending 
currents the anode is above, and since the closing shock origi- 
nates at the kathode (below), the stimulus does not have to pass 
through this area of diminished conductivity ; but on opening 
the current the shock originates at the anode (above), and since 
now the area of the kathode possesses a very much diminished 
power of conductivity, the impulse does not reach the muscle. 
On the other hand, in ascending currents the closing stimulus 
(kathodic) originates above and must pass through the area of 
diminished conductivity (at the anode) if it reach the muscle 
at all — which it does not do, and there is consequently no con- 
traction on closing ; but on opening the current the shock origi- 
nates at the anode (below) and passes without interruption to 
the muscle. These phenomena are, therefore, fully explained 
by the fact that the region of the kathode loses its conducting 
power during the flow of a strong current, and the region of the 
anode loses its conducting power at the instant such a current is 
withdrawn. 

5. It has already been noticed that the uninterrupted flow of 
an electric current through a nerve is unattended by muscular 
contraction ; it has likewise been seen that very slow changes in 
the strength of the current are similarly unaccompanied by the 
manifestations of ordinary stimulation ; but sudden changes in 
the strength, whether in the direction of increase or decrease, act 
as stimuli. However, while the passage of a constant current 
through a nerve does not manifest itself by contractions except 
at making and breaking, such a passage brings about a change 
in the tissue of the nerve known as electrotonus. It may be 



304 THE NERVOUS SYSTEM. 

considered a state of electric tension. In the anodic area the 
excitability is diminished (anelectrotonus); in the kathodic area 
it is increased (katelectrotonus). Nor is the electrotonic con- 
dition restricted to that portion of the nerve between the poles. 
Between the poles there is a point where the two influences — 
anelectrotonus and katelectrotonus — meet and there is neither 
increased nor decreased excitability. With weak currents this 
point is nearer the anode ; with strong ones nearer the kathode. 
A descending current diminishes the excitability of a nerve ; an 
ascending increases it. Prolonged application of electric stimuli 
will exhaust nervous excitability, but it may be restored by rest, 
or more quickly by an opposite current. 

(The foregoing facts regarding electric stimulation are drawn 
largely from the American Text-Book of Physiology. ) 

THE CEREBRO-SPINAL AXIS. 

The cerebro -spinal axis embraces the nervous matter in the 
cranial cavity and in the spinal canal, excepting the roots of the 
cranial and spinal nerves. This axis consists of both white and 
gray matter. The white matter is made up of conducting ele- 
ments ; the gray matter consists of a number of connected 
ganglia. In the cord the white matter is situated externally ; in 
the brain the gray. The encephalon is situated in the cranial 
cavity and consists of the cerebrum, the cerebellum, the pons 
Varolii, and the medulla oblongata. These different parts are 
connected with each other and with the cord by nerve fibers, 
and all the cranial and spinal nerves are connected with gray 
matter either in the brain or in the cord, or in both. This gray 
matter exists for the purpose of receiving impressions and gen- 
erating nerve force. 

Membranes. — The encephalon and cord are covered by mem- 
branes for protection and for the support of vessels belonging 
thereto. These are (1) the dura mater, (2) the arachnoid and 
(3) the pia mater. 



THE SPINAL CORD. 305 

The dura mater is a dense fibrous structure surrounding the 
encephalon and adherent to the inner surfaces of the cranial 
bones. At certain points the two layers of which it is composed 
separate to form the venous sinuses. Processes of the internal 
layer also are sent inward between the two lobes of the cere- 
brum (falx cerebri), between the cerebrum and cerebellum (ten- 
torium cerebelli), and between the lateral halves of the cerebel- 
lum (falx cerebelli). This membrane passes through the fora- 
men magnum to cover also the spinal cord, and to follow as a 
sheath the spinal nerves at their foramina of exit. 

The arachnoid resembles the serous membranes. It covers 
the brain and cord underneath the dura mater without dipping 
into the sulci of the brain. Between it and the pia mater is 
what is known as the subarachnoid space containing the sub- 
arachnoid fluid. This fluid serves a mechanical purpose, equal- 
izing pressure in different parts of the cerebro-spinal axis and 
protecting the nervous substance from injury by concussion, etc. 
Besides being found in the subarachnoid space, it occupies the 
ventricles of the brain and the central canal of the cord, com- 
munication between these being furnished by a small opening at 
the inferior angle of the floor of the fourth ventricle. 

The pia mater is a very delicate structure dipping between the 
convolutions of nervous matter and lying in close contact with 
the external surface of the encephalon and cord. It is exceed- 
ingly vascular ; indeed its main function is to support vessels be- 
longing to the nervous substance underneath. Both the arach- 
noid and the pia mater pass out at the foramen magnum with 
the dura to cover the cord. 

The Spinal Cord. 

The spinal cord occupies the spinal canal and is about eigh- 
teen inches long, extending from the foramen magnum to the 
lower border of the first lumbar vertebra. Its distal extremity is 
in the shape of a slender filament known as the filurn terminate, 



306 



THE NERVOUS SYSTEM. 



which is gray in color. The sacral and coccygeal nerves, having 
taken origin from the cord in the dorsal region, pass downward 
in the canal to find exit through the sacral and coccygeal fora- 
mina. This collection of nerves thus passing down is known as 
the cauda equina. 

Gross Divisions of the Spinal Cord in Section. — Cross section 
of the cord reveals the division of its substance into two lateral 
halves connected by the anterior and posterior commissures. In 

Fig. 70. 




Different Views of a Portion of the Spinal Cord from the Cervical Re- 
gion, with the Roots of the Nerves. (Slightly Enlarged.) 
In A, the anterior surface of the specimen is shown ; the anterior nerve-root of its right 
side is divided ; in B, a view of the right side is given ; in C, the upper surface is shown ; in 
D, the nerve-roots and ganglion are shown from below. 1, the anterior median fissure ; 2, 
posterior median fissure ; 3, anterior lateral depression, over which the anterior nerve-roots 
are seen to spread ; 4, posterior lateral groove, into which the posterior roots are seen to 
sink; 5, anterior roots passing the ganglion; 5', in A, the anterior root divided; 6, the 
posterior roots, the fibers of which pass into the ganglion 6' ; 7, the united or compound 
nerve; 7', the posterior primary branch, seen in A and D to be derived in part from the an- 
terior and in part from the posterior root. {Kirkes after Allen Thomson.) 



THE SPINAL CORD. .307 

the center of the cord, and between these commissures, is a small 
opening, the central canal of the cord, communicating with the 
fourth ventricle above. This division of the substance of the 
cord into lateral halves is effected by the two median fissures, 
anterior and posterior. The former is the more clearly marked, 
and is lined throughout with pia mater. It is bounded pos- 
teriorly by the anterior white commissure. The posterior median 
fissure is not lined with pia mater and extends anteriorly as far 
as the posterior gray commissicre. It is to be noted that there 
are both anterior and posterior gray commissures, but only one 
white commissure (anterior), which is bounded posteriorly by 
the anterior gray commissure. 

Besides the anterior and posterior median fissures there are 
also on each side anterolateral and posterolateral fissures, mark- 
ing the lines of exit of the anterior and posterior roots of the 
spinal nerves. These are not well defined. They divide the 
cord into anterior, posterior and two lateral columns. 

Arrangement of Gray Substance. — The disposition of the 
gray substance in the cord (in tran verse section) is somewhat 
after the manner of the letter H, each lateral portion represent- 
ing the anterior and posterior cornua of gray matter for that side, 
and being connected to the corresponding portion of the other 
side by the commissures embracing the central canal. The an- 
terior cornua are shorter and thicker than the posterior. From 
these issue the anterior and posterior roots respectively of the 
spinal nerves. The cells are : ( i ) Those in the anterior cornu ; 
(2) those in the posterior cornu; (3) those in the lateral aspect 
of the gray matter ; (4) those at the inner base of the posterior 
cornu (Clarke's vesicular column). 

The gray substance is made up of cells with, of course, the 
usual neuroglia and blood-vessels. The cells in the anterior cornua 
are larger in size and possess a greater number of poles than 
those in the posterior cornua ; from their connection with the 
anterior (motor) spinal nerve roots they are called motor cells 



3 o8 



THE NERVOUS SYSTEM. 



in contradistinction to the sensory cells in the posterior cornua 
which are connected indirectly with the posterior (sensory) nerve 
roots. 

Degeneration. — Nerve fibers when separated from the cells 
of which they are outgrowths degenerate. Fibers have been 
said to degenerate in the direction in which they carry messages, 
but this is by no means always so. For instance, the parent cells 
for the fibers of the posterior spinal roots are in the ganglia on 
those roots near the cord, and section of the root beyond the 
ganglion causes degeneration of its fibers peripherally — which 
is in the opposite direction to the passage of impressions in them. 

Fig. 71. 




Diagram to Illustrate Wallerian Degeneration of Nerve-Roots. (Kirkes.) 

Section of the posterior root between the ganglion and cord is 
followed by centripetal degeneration, and there is no centrifugal 
degeneration. The a?iterior spinal root fibers are outgrowths of 
cells in the anterior cornua of gray matter. Section of this root 
anywhere occasions centrifugal degeneration (Fig. 71). 

Arrangement of the White Substance. — It is scarcely neces- 
sary to state that the white substance of the cord consists of 



THE SPINAL CORD. 



3°9 



nerve fibers with their usual accompaniments. It is external to 
the gray. The fibers are medullated, but have no sheath of 
Schwann. 

The divisions of the cord already referred to are purely ana- 
tomical. Physiological and pathological researches warrant the 
further division of the white substance of the cord into eight 
columns for each side. The course of all the fibers in the white 
matter of the cord is by no means certain. The division here 
given may not be strictly correct, but it probably receives as 
little adverse criticism as any of the others. Classified accord- 
ing to the direction in which their fibers degenerate after section 
the paths are : (I.) Degenerating downward, (a) the column of 

Fig. 72. 
a b 




Scheme of the Conducting Paths in the Spinal Cord at the 3D Dorsal 

Nerve. 
The black part is the gray matter. V, anterior, hw, posterior root ; a, direct, and 'g, 
crossed, pyramidal tracts ; b, anterior fundamental fasciculus ; c, Goll's column ; d, column 
of Burdach ; e, anterior radicular zone; f mixed lateral tract; h, direct cerebellar tracts. 
{Landois, modified.) 

Turck and (&) the crossed pyramidal tract; (II.) degenerating 
upward, {a) the column of Goll and (£) the direct cerebellar 
tract; (III.) degenerating in neither direction, {a) the anterior 
fundamental fasciculus, (o) the anterior radicular zone, (V) the 
mixed lateral column and (d) the column of Burdach. 

I. (a) The colunin of Turck occupies a position just lateral to 



310 THE NERVOUS SYSTEM. 

the anterior median fissure and extends downward to the lower 
dorsal region. Its fibers decussate high up in the cord. This 
column is sometimes called the direct, or uncrossed, pyramidal 
tract, as distinguishing it from the other descending column. 
(/?) The crossed pyramidal tract is external to the posterior cornu 
of gray matter and internal to the direct cerebellar tract. Its 
fibers decussate in the anterior pyramids of the medulla oblongata. 

II. (a) The direct cerebellar tract occupies the outer posterior 
part of the lateral column. Its fibers reach the cerebellum 
through the inferior peduncles, after having traversed the poste- 
rior pyramids of the medulla. This tract exists throughout the 
length of the cord. (^) The column of Goll (postero-internal 
column) is situated posteriorly in a position corresponding to 
the column of Turck anteriorly — just lateral to the posterior 
median fissure. Fibers in this column extend from the upper 
lumbar region to the funiculi graciles of the medulla. 

III. (a) The anterior fundamental fasciculus lies between the 
column of Turck internally and the anterior cornu and anterior 
roots of the spinal nerves externally. Its fibers are lost in the 
medulla above. (I?) The anterior radicular zo?ie is external to 
the anterior roots of the spinal nerves and anterior to the crossed 
pyramidal tract and the direct cerebellar fasciculus. Its fibers 
are lost in the medulla above. (V) The mixed lateral column is 
just external to the main body of gray matter and does not 
reach the surface of the cord. Its fibers are likewise lost in the 
medulla oblongata. (V) The colum7i of Burdach (postero-ex- 
ternal column) is situated posteriorly in a location corresponding 
to the anterior fundamental fasciculus anteriorly — external to the 
column of Goll and internal to the posterior cornu. Its fibers 
reach the cerebellum through the inferior peduncles, having 
passed through the restiform bodies. 

Functions of the Columns. — Remarks already made touching 
the direction of degeneration in the separate columns throw some 
light upon the physiological function of the fibers in each. 



THE SPINAL CORD. 



311 



Motor impulses pass downward from the brain through cer- 
tain fibers to the cells of the anterior cornua of .gray matter in 
the cord, and are sent thence through the spinal nerves to the 
muscles. The paths in the cord conveying these impulses are 

Fig. 73. 




m lib 

Course of the Fibers for Voluntary Movement. 

ab, path for the motor nerves of the trunk ; c, fibers of the facial nerve ; B, corpus cal- 

losum ; Nc, nucleus caudatus ; G. i, internal capsule ; N. I, lenticular nucleus ; P, pons ; N.f, 

origin of the facial ; Py, pyramids and their discussion ; 01, olive, Gr, restiform body ; PR, 

posterior root ; AR, anterior root ; x, crossed, and z, direct pyramidal tracts. {Landois .) 



312 THE NERVOUS SYSTEM. 

found to be the columns of Turck and the crossed pyramidal 
tracts, and these are the only parts of the cord known so to act. 
Impulses to the upper segment of the cord may be conveyed by 
either of these columns, but impulses to the lower segment must 
follow the crossed pyramidal tract, since the column of Turck 
ceases to exist in the dorsal region. Only some 3-7 per cent, 
of motor fibers from the cortex are thought to enter the columns 
of Turck. The others decussate in the medulla and enter the 
crossed pyramidal tracts. In any case motor impulses originat- 
ing in the brain and so conveyed are manifested on the side 
opposite their cerebral origin, since the fibers in both these tracts 
decussate in passing downward. It is a well known pathological 
fact that lesions of motor areas in the brain, or section of one 
lateral half of the cord, are followed by paralysis on the side 
opposite the lesion. 

Following a motor fiber (A, Fig. 74) through the anterior root 
of a spinal nerve, it is found to originate from one of the large 
multipolar cells (3) in the anterior cornu of gray matter. Around 
these anterior horn cells (1, 2, 3, 4) arborize the end filaments 
of fibers which have come down through the cord from the brain. 
Some fibers have come down in the uncrossed pyramidal tract 
(column of Turck) on the side opposite the cells 1, 2, 3, 4, and 
crossed over to the same side through the anterior white com- 
missure approximately on a level with the cells ; others have de- 
cussated in the medulla, and come down in the crossed pyramidal 
tract on the same side as the cells. In both cases the fibers or- 
iginated in the brain on the side opposite the cells around which 
they arborize in the cord. This is the connection which exists 
between the brain and the anterior root fibers. 

Not all fibers in the anterior nerve roots are thus prolonged 
upward in the pyramidal tracts. The number of fibers in these 
roots is much larger than in the pyramidal tracts, and conse- 
quently some of them must end (originate) directly in the cells 
of the anterior cornua. Furthermore, it seems that some fibers 



MOTOR PATHS IN THE CORD. 



3 1 3 



pass from the anterior nerve roots directly into the pyramidal 
tracts without being interrupted by motor cells. 

Fig. 74. 




Course of Nerve-Fibers in Spinal Cord. ( Kirke after Schafer. ) 

The column of Turck and the crossed pyramidal tract are, 
therefore, the motor paths in the cord. 

Fibers entering the cord by the posterior roots send prolonga- 
tions both upward and downward in the gray matter of the cord, 
and communicate by end arborizations with the small sensory 
cells in the posterior cornua and with cells in several other lo- 
calities. (See Figs. 74, 81.) Reference to Fig. 74 will show 
that the connection of the anterior nerve fibers with the gray 
matter of the cord is simple, while that of the posterior is com- 
paratively complex. 1, 2, 3, 4 are anterior horn cells. Each of 



314 



THE NERVOUS SYSTEM. 



these gives rise to an efferent fiber, one of which (A) is shown 
distributed to a muscle (M). Each of these cells also is sur- 
rounded by the end arborization of a fiber (P) from the cortex. 
A fiber from the posterior root is also shown. It originates 

Fig. 75. 




Transverse Section Through Half the Spinal Cord, Showing the Ganglia. 

A, anterior cornual cells; B, axis-cylinder process of one of these going to posterior root; 
C, anterior (motor) root; D, posterior (sensory) root; E, spinal ganglion on posterior 
root; F, sympathetic ganglion; G, ramus communicans ; H, posterior branch of spinal 
nerve ; I, anterior branch of spinal nerve ; a, long collaterals from posterior root fibers 
reaching to anterior horn; a, short collaterals passing to Clarke's column ; c, cell in Clarke's 
column sending an axis-cylinder process (d) to the direct cerebellar tract ; e, fiber of the an- 
terior root ; f, axis cylinder from sympathetic ganglion cell, dividing into two branches, one 
to the periphery, the other towards the cord ; g, fiber of the anterior root terminating by an 
arborization in the sympathetic ganglion ; h, sympathetic fiber passing to periphery. 
( Ki r ke af t er Ramon y Caja I. ) 

in a cell of the sensory ganglion ( G). It bifurcates, one branch 
going to the surface (£*), the other enters the cord and itself 
bifurcates. The branch (E) is short and arborizes around a 
small cell (/\) in the posterior cornu, from which a new axis 



SENSORY PATHS IN THE CORD. 315 

cylinder arises to arborize around the anterior horn cell (4). 
The other branch (D) travels upward in the posterior column 
of the cord. A collateral (5) is seen going to the anterior horn 
cell (2), one to the posterior horn cell (P 2 ) and another to a 
cell (C) in the inner base of the posterior cornu (in Clarke's col- 
umn) ; from Can axis-cylinder enters the direct cerebellar tract. 
The main fiber (8) may terminate in the gray matter of the 
cord above, or in the medulla. Impressions brought thus to the 
cord are carried to the opposite side and pass up through the 
gray matter in most part. The fibers decussate at no particular 
point, but throughout the length of the cord. However, some 
fibers bearing sensory impressions pass to the column of Goll 
and thus upward, while some also go to the encephalon by the 
direct cerebellar fasciculi and the columns of Burdach. Ex- 
perimentally, decussation of sensory fibers is demonstrated (1) by 
longitudinal section of the spinal cord in the median line, which 
is followed by anesthesia on both sides below the section ; and (2) 
by horizontal section of one -half of the cord, which is followed 
by anesthesia on the opposite side below the section. It is 
claimed that pain and temperature sensations decussate at once 
on reaching the gray matter, while sensations of touch, pressure 
and equilibration pass up on the same side until the medulla is 
reached. Some afferent fibers are probably not continued upward 
to the brain either directly or indirectly. 

It thus appears that we have no very accurate knowledge of 
the sensory paths in the cord. The gray matter seems princi- 
pally concerned ; but the columns of Goll and Burdach and the 
direct cerebellar fasciculi also convey afferent impressions. For 
both motor and sensory paths to the cortex see p. 337. 

The columns of Burdach have been said to present no degen- 
eration secondary to section. Trophic centers for their fibers 
must, therefore, exist both above and below any given point of 
section. It is found that the fibers constituting these columns 
pass in and out along the cord between cells in different planes 



31 6 THE NERVOUS SYSTEM. 

and acting as longitudinal commissural fibers. In locomotor 
ataxia the characteristic symptom is inability to coordinate the 
muscular movements — especially of the lower extremities ; the 
characteristic lesion has been found to be in the columns of Bur- 
dach. This is of importance in determining the function of these 
columns, and, in fact, leads to the conclusion that their fibers 
assist in regulating and coordinating the voluntary movements. 
This opinion is further supported by the connection of these 
fibers with the cerebellum, which contains the center for muscular 
coordination — if such a center exist. The sense of pressure and 
the so-called muscular sense are probably connected with the 
fibers of this column, and these may be the only sensory impres- 
sions conveyed through the columns of Burdach. 

The anterior fundamental fasciculi, the anterior radicular 
zones, and the mixed lateral paths degenerate in neither direc- 
tion after section, their trophic cells existing at both extremities. 
They connect cells in the gray matter of the cord. 

Functions of the Spinal Cord. — These are (i) conduction, 
(2) transference, (3) reflex action, (4) augmentation, (5) 
coordination, (6) inhibition of reflex acts, (7) special cen- 
ters (Collins and Rockwell, modified). 

1. Conduction. — This has been referred to in discussing the 
white columns of the cord. This function makes it possible for 
the brain to receive impressions from and send impulses to the 
periphery. It is to be remembered that most of these impres- 
sions and impulses are interrupted by spinal nerve cells in their 
passage between brain and periphery. 

2. Transference. — An impression reaching the gray matter of 
the cord may be transferred (not as in typical reflex action) so 
as to be felt in an entirely different region from that in which 
the irritation takes place. Hip joint disease often gives pain in 
the knee alone. 

3. Reflex Action. — The cord may act as a center without the 
cooperation of the brain. Indeed, by no means do muscular 



REFLEX ACTION. 317 

movements cease immediately on removal of the encephalon if 
the cord and its nerves be left intact. An animal so mutilated 
possesses no sensation or volition, but for a time the sensory 
nerves will continue to convey impressions and the motor nerves 
impulses. Under these conditions impressions (as of heat) are 
conveyed to the cord by the afferent nerves ; the gray matter of 
the cord receives the impressions and generates motor force 
which is sent out through the corresponding efferent nerves, and 
movements result. This is reflex action. The impression is 
reflected through the cord and manifested in motion without the 
intervention of sensation or volition. Reference to Figs. 74 and 
81 shows how reflex action is anatomically possible through the 
cord connections. Typical reflex action requires anatomically 
(1) something to produce an impression, (2) a nerve terminal to 
receive it, (3) a centripetal fiber to convey it, (4) a center to 
receive and transform it, (5) a centrifugal fiber to convey it to 
the periphery and (6) a muscle to contract. This remark 
applies to reflex action connected with the cord, but by common 
consent reflex action is not limited to the cord and its connections. 

If reflex action be defined as any involuntary manifestation of 
nerve force consequent upon the reception of an impression 
(general or special) by a nerve center, the term must be made 
to include such phenomena as intestinal peristalsis, contraction 
and dilatation of the pupil, certain mental operations, etc. In 
reality most reflex acts are of a complex nature, involving asso- 
ciated action on the part of several neurons and being manifested 
frequently at several points. For example, a foreign body in the 
larynx causes reflexly not only closure of the glottis, but also the 
convulsive muscular contractions incident to coughing. The 
realm of reflex action is obviously a wide one. 

It may be said that ordinary reflexes are usually under the 
direction of the cord, but this does not imply that the brain 
may not be concerned. Pricking the sole of the foot of a sleep- 
ing person will cause him to draw up his leg without the interven- 



318 THE NERVOUS SYSTEM. 

tion of consciousness. Probably were he awake the withdrawal 
would still be a reflex ; but he would certainly be conscious of 
the pain, though after the act of withdrawal was accoinplished. 
Nor is reflex action by any means limited to the cerebro-spinal 
system. Either of the two systems, or both, may be concerned. 

Now in order for reflex movements to occur, there must be a 
transference of impressions received by sensory cells to cells 
capable of giving origin to motor impulses. The cells communi- 
cate by their collaterals, which may be short or long, depending 
on the distance between the cells concerned. Cells in the gray 
matter of the cord are ' ' connected ' ' by such fibers, and they 
run largely in the white matter of the cord joining cells on 
different planes. They constitute the larger part of the anterior 
fundamental fasciculi, the anterior radicular zones, and the 
mixed lateral tracts, and it is these paths which are mainly con- 
cerned in reflex action of the cord. 

4. Augmentation. — Sensory fibers, on reaching the cord, send 
prolongations both upward and downward in the gray matter. 
These prolongations, by their end arborizations, seem to com- 
municate indirectly with several motor cells. In the simplest 
reflex movements connected with the spinal cord the muscular 
activity is limited to the area corresponding to the distribution 
of the afferent nerve which has been irritated \ but if the irrita- 
tion be sufficiently increased other muscles in the same locality, 
or the corresponding muscles on the opposite side of the body, 
or even the whole musculature, may be thrown into action. 
This is explained on the ground that under favorable conditions 
of central excitability, strength of peripheral irritation, etc., the 
afferent impression is disseminated by collaterals throughout a 
large area of the cord (for example), and a large number of ef- 
ferent cells are made to discharge. The reflex excitability of 
the cord is markedly increased by the administration of such 
drugs as strychnin. An animal so poisoned will be thrown into 
the most violent convulsions by so slight a sensory impression as 



3 1 9 

a simple breath of air. Removal of the encephalon in inferior 
animals also exaggerates reflex excitability. 

5. Coordination. — This has been referred to under the 
columns of Burdach. Coordination is " a repetition of ordinary 
reflex acts for our daily lives." No effort is necessary to coor- 
dinate the muscular movements of deglutition, respiration, walk- 
ing, etc. These movements may be performed when the cere- 
brum is removed. 

6. Inhibition of Reflex Acts. — This is not a function of 
the cord proper, but is directed by the cerebrum. A great 
many reflex movements may be inhibited by an act of the will, 
providing always they are due to contraction of striped muscle. 
The reflex acts of coughing or sneezing, or those resulting from 
tickling, for example, can be largely controlled. These are 
usually performed as reflex cord acts, but the brain may evidently 
assert its superiority over the cord and inhibit them. 

7. Special Centers. — In the gray matter of the cord are found 
various centers for distinct acts such as defecation, parturition, 
micturition^ etc. These are all connected with each other and 
with the encephalon and obey the usual laws of reflex action. 

THE ENCEPHALON. 

The encephalon is situated within the cranial cavity and is 
commonly called the brain. Its gross divisions are the medulla 
oblongata, the pons Varolii, the cerebellum, and the cerebrum. 
All the other divisions are in a measure subordinate to the cere- 
brum, though each division has individual functions. The 
human brain weighs about 49^ ounces in the male and about 
44 in the female. 

The Medulla Oblongata. 

Anatomy. — The medulla oblongata, or bulb, joins the upper 
extremity of the spinal cord and extends to the pons above. It 
has a pyramidal shape, lies in the basilar groove of the occipital 
bone, and is slightly flattened antero-posteriorly. It is about an 



320 



THE NERVOUS" SYSTEM. 



inch and a quarter in length, half an inch thick, and three 
quarters of an inch broad above. The anterior and posterior 
median fissures of the cord are continued upward in the medulla ; 
the central canal terminates in the inferior angle of the fourth 
ventricle. The anterior columns appear to be continuous with 
the anterior pyramids of the medulla. These pyrai?iids are situ- 
ated just lateral to the anterior median fissure. The innermost 

Fig. 76. 




Floor of the 4TH Ventricle and the Connections of the Cerebellum. 
On the left side the three cerebellar peduncles are cut short ; on the right the connections 
of the superior and inferior peduncles have been preserved, while the middle one has been 
cut short. 1, median groove of the 4th ventricle with the fasciculi teretes ; 2, the striae of the 
auditory nerve on each side emerging from it ; 3, inferior peduncle ; 4, posterior pyramid 
and clava, with the calamus scriptorius above it ; 5, superior peduncle; 6, fillet to the side of 
the crura cerebri ; 8, corpora quadrigemina. {Landois.) 

fibers of the pyramids are the continuations upward of the 
crossed pyramidal tracts, and are seen to decussate in the median 
line ; the outermost fibers are the prolongations of the uncrossed 
pyramidal tracts. The olivary bodies, oval in shape, are just ex- 
ternal to the anterior pyramids separated from them by a groove. 
The restiform bodies make up the postero-lateral portion of the 



THE MEDULLA OBLONGATA. -321 

medulla, and are external to the olivary bodies. They contain 
fibers from the columns of Burdach, and contribute largely to 
the formation of the inferior peduncles of the cerebellum. The 
restiform bodies, diverging as they ascend, form the lateral 
boundaries of the inferior division of the fourth ventricle. Be- 
neath the olivary bodies, and between the anterior pyramids and 
the restiform bodies, are the lateral fasciculi, or the funiculi of 
Rolando. They constitute the upward prolongation of all the 
antero -lateral portion of the cord which does not go to the for- 
mation of the anterior pyramids. Their chief importance is in 
the fact that they contain the centers for respiration. The pos- 
terior pyramids are sometimes called the funiculi graciles. They 
join the restiform bodies and pass to the cerebellum. 

The fourth ventricle deserves particular attention. It is a 
cavity on the posterior aspect of the pons and medulla extending 
from the upper limit of the former to a point on the latter oppo- 
site the lower border of the olivary body. It has the shape of 
two isosceles triangles placed base to base. The apex of the 
inferior triangle is at the calamus scriptorius, and its lateral 
boundaries are the diverging restiform bodies. The superior 
peduncles of the cerebellum form the lateral boundaries of the 
superior triangle. The inferior triangle is covered by the 
cerebellum ; the superior by the valve of Vieussens, which 
stretches between the superior peduncles. This ventricle com- 
municates above with the third ventricle by the aqueduct of 
Sylvius, or the iter a tertio ad quartum ventriculum ; below, with 
the central canal of the cord and with the subarachnoid space. 
The floor of the ventricle presents a longitudinal median fissure 
and numerous small elevations indicating the position of the 
nuclei of origin of certain of the cranial nerves. 

The gray matter of the medulla has the same general distri- 
bution as that in the cord, but is by no means so regular in its 
disposition. The direction of the white fibers is not so uniform 
as in the cord. They run not only longitudinally, but trans- 
21 



32 2 THE NERVOUS SYSTEM. 

versely to connect the lateral halves, and in other directions to 
connect various centers situated in this part of the encephalon 
and to connect the medulla with other parts of the brain. The 
following is the relation of the columns of the cord to the 
medulla : 

The dh'ect and crossed pyramidal tracts pass to the encephalon 
constituting, in the medulla, the anterior pyramids — the direct, 
having decussated below, occupying here the outer portion of 
the pyramid, and the crossed decussating in the medulla and oc- 
cupying the inner portion of the pyramid. 

Those columns concerned in reflex action, the anterior funda- 
mental fasciculi, the anterior root zones, and the mixed lateral 
tracts do not continue farther upward than the gray matter of 
the medulla. 

The columns of Goll are continuous with the funiculi graciles. 

The columns of Burdach and the direct cerebellar fasciculi 
pass to the cerebellum through the restiform bodies of the 
medulla. 

Functions. — The functions of the medulla are (i) conduction, 
(2) reflex action, (3) to furnish centers for special acts. 

1 . As a conductor the medulla is absolutely necessary as a means 
of connection between the brain and cord. Sensory impressions 
to and motor impulses from the brain must all pass through by 
this route. 

2. As a reflex nerve center the medulla also resembles the cord, 
though impressions reflected through this organ are frequently 
much less simple than those reflected through the cord. Reflex 
action in the medulla is dependent on (3), to be noticed 
now. 

3. The most important center presiding over coordinated move- 
ments is that for respiration. The encephalon may be cut away 
down as far as the medulla, and life will continue for a certain time. 
It is also true that the medulla itself may be gradually cut away 
from above downward until a certain point is reached, when res- 



THE PONS VAROLII. .323 

piration suddenly ceases. Likewise the spinal cord may be cut 
away upward till this point is reached, when the- same result will 
follow. This is the true respiratory center, and is situated at 
the site of origin of the vagi. Its destruction is followed by 
an immediate suspension of respiration and consequent death by 
asphyxia, though there is no manifestation of the distress usually 
accompanying this condition. The sense of want of air is sim- 
ply lost. There is one of these centers for each side, but they 
act synchronously, being connected by commissural fibers. Prob- 
ably the usual mode of stimulation of the respiratory center is 
by afferent impressions, but it may also be stimulated directly, as 
by deoxygenated blood. Mutilation of the medulla, on account 
of the presence of this center, is followed by the nearest approach 
to instantaneous death, and the respiratory center has, therefore, 
been called the " vital spot," though death from any cause can- 
not be instantaneous. 

Some other reflex centers are for deglutition, sticking, secretion 
of saliva y vomiting, coughing, sneezing, dilatation of the pupil, se- 
cretion of sweat, secretion of glycogen, etc. Typical of these is 
the reflex act of sneezing, in which case impressions are conveyed 
to the medulla by the nasal branches of the fifth nerve. 

Additional centers in the medulla are those which preside over 
inhibition and acceleration of the heart, vasomotor centers for the 
vessel walls, and centers for special senses like hearing and taste. 
There is also said to be here a center controlling the production 
of heat by the tissues. 

The Pons Varolii. 

Anatomy. — The pons is situated just above the medulla ob- 
longata at the base of the brain, and is frequently called the 
great commissure, for the reason that it contains white fibers con- 
necting the two lateral halves of the cerebellum and the differ- 
ent portions of the cord and medulla with the parts of the brain 
above. It resembles the cord in having its white matter situ- 
ated externally, while within its substance are a number of 



324 THE NERVOUS SYSTEM. 

collections of gray matter. The longitudinal fibers are con- 
tinuations upward of fibers from the olivary bodies and the an- 
terior pyramids of the medulla and also of parts of the poste- 
rior and lateral columns of the cord. They pass through the 
crura cerebri to the brain. 

Functions. — The anatomical structure and situation of the 
pons at once suggest that its function is to transmit motor im- 
pulses from and sensory impressions to the cerebrum. 

The gray centers, however, indicate a further function of this 
organ. It is found that the removal of all parts of the enceph- 
alon above the pons does not deprive an animal of voluntary 
motion and general sensibility. It will be seen later that the 
integrity of the cerebrum is essential to any intellectual opera- 
tion, and manifestly, under the conditions mentioned, there can 
be no voluntary motion which indicates any degree of intelli- 
gence ; but the fact remains that the animal can perform 
movements which are different from the reflex movements de- 
pending on the presence of the cord when all other parts of the 
cerebro- spinal axis have been removed. The pons is apparently 
* ' an organ capable of originating impulses giving rise to vol - 
untary movements, when the cerebrum, corpora striata and 
optic thalami have been removed, and it probably regulates the 
automatic voluntary movements of station and progression." 
(Flint.) 

Nor can it be doubted that an animal thus mutilated feels 
pain. It is probable that the sensory impression is received by 
some of the gray centers in the pons itself, but not being con- 
veyed to the cerebrum, is not remembered. 

The Crura Cerebri, Corpora Striata, Optic Thalami, Internal 
Capsule and Coipora Quadrigemina. 
It will be well before discussing the cerebrum to consider 
briefly other collections of gray and white matter in the neigh- 
borhood of the upper part of the pons. 



THE BASAL GANGLIA. 



525 



The crura cerebri, passing upward from the anterior part of 
the pons, diverge to run apparently underneath the corpora 

Fig. 77. 



Cornu'anticum. 



Caputnuclet "caudatt. 



Capsula externa. 
. Island of Reil. 

— Nucleus lentifomus. 
L— Claustrurru 




Capsula interna - 
(posterior limb). 
Thalamus opticus 



Funiculus ci 
■ Tuniculusgracilis, 

Human Brain, with the Hemispheres; Removed by a Horizontal ^Incision on 

the Right Side. 

4, trochlear; 8, acoustic nerve; 6, origin of the abducens ; F, A, L, position of the pyra- 
midal (motor) fibers for the face, arm and leg; S, sensory fibers. (Landoz's.) 



striata and optic thalami in the direction of the cerebral hemis- 
pheres. They are about fy inch long and slightly broader 
above than below. The main bulk of each crus consists of 



326 THE NERVOUS SYSTEM. 

white fibers , but a collection of gray matter (locus niger) divides 
the band into a lower or superficial section, called the crusta, and 
an upper or deep section, called the tegmentum. There is also 
some gray matter in the tegmentum proper. The fibers of the teg- 
mentum are supposed to convey afferent impressions chiefly, and 
end for the most part in the optic thalamus, though some are con- 
tinued to the cerebrum through the internal capsule. The fibers 
of the crusta are supposed to convey efferent impulses, and pass 
to the corpus striatum and the cerebrum. 

It is evident that the function of the crura is mainly to con- 
duct messages to and from the parts above. It is said that the 
locus niger is concerned in coordination of the movements of 
the eye-ball and iris. 

The Corpora Striata, Optic Thalami and Internal Capsule 
are closely related and are best considered together. 

Each corpus striatum is pear-shaped with its large end forward 
and near the median line \ the posterior small extremities are 
divergent from each other and embrace the two optic thalami. 
Externally they are white ; internally white and gray elements 
are mixed. Each is separated by the anterior limb of the 
internal capsule into two divisions, external and internal, 
known respectively as the lenticular and caudate nuclei. (See 
Fig. 77.) 

The optic thalami, one on either side, have an oval shape and 
rest upon the crura cerebri between the posterior extremities of 
the two corpora striata. • Most of their external surface is white \ 
internally each possesses six gray nuclei. 

Separating the two nuclei of the corpus striatum anteriorly, 
and the lenticular nucleus from the optic thalamus posteriorly, is 
a band of white fibers known as the internal capsule. The part 
between the two nuclei is the anterior limb ; that between the 
lenticular nucleus and the optic thalamus is the posterior limb. 
These limbs, joining at an obtuse angle, constitute a bend in the 
internal capsule which is called the genu, or knee. The fibers 



THE BASAL GANGLIA. 327 

of the capsule pass to the frontal, parietal and occipital lobes of 
the cortex, and in their course to these parts .they diverge to 
form the corona radiata. 

External to the lenticular nucleus is a band of white fibers 
known as the external capsule. In it is a longitudinal mass of 
gray matter, the claustrum. Fig. 77 shows the relations of 
these parts. 

Functions. — The exact function of the corpora striata is a 
matter of some doubt. They have been considered the great 
motor ganglia of the base of the brain ; but, although lesions 
here are followed by paralysis on the opposite side of the body, 
it is held that this phenomenon is due to the proximity of the 
internal capsule. The further fact that irritation of this organ 
is followed by muscular contractions does not prove that it 
ordinarily generates motor force, for many of the fibers from the 
motor cortical zone pass to or through the corpus striatum. 
This may be only a relay station, and the corpus may be quite 
subsidiary. It undoubtedly, however, is connected with motion 
in some way. 

The precise function of the optic thalami is equally obscure. 
The relation of these organs to the tegmenta would suggest that 
they have something to do with the sensory fibers on their way 
to the cortex. It cannot be denied that they are concerned in 
sensation, since their removal is followed by crossed anesthesia. 
They may likewise be relay stations. Each sends fibers to the 
cerebellum and contains one of the nuclei of origin of the optic 
nerve. 

Regarding the function of the internal capsule it may be said 
that its fibers are in main part prolongations from the crusta and 
from the gray matter of the corpora striata ; fibers also pass up- 
ward through it from the tegmentum and the optic thalamus. As 
a matter of fact, most of the fibers of the crura go directly into 
the corpora striata (motor) and the optic thalami (sensory), but 
some pass directly upward through the capsule. It is to be 



328 THE NERVOUS SYSTEM. 

noted, however, that the capsule does not consist of these last 
named fibers alone, but of fibers from the corpora striata and 
optic thalami as well. Observations show that pathological 
lesions affecting the anterior two thirds of the posterior division 
of the internal capsule are followed by paralysis of motion ; that 
lesions affecting only the posterior one third of the posterior 
division are followed by anesthesia ; and that lesions affecting 
the entire posterior limb are followed by both paralysis and 
anesthesia — these phenomena always manifesting themselves on 
the side opposite the lesion only. This leads to a definite con- 
clusion ; viz., that efferent fibers occupy the anterior two thirds 
and afferent fibers the posterior one third of the posterior limb 
of the capsule. 

Nothing conclusive can be said about the function of the ex- 
ternal capsule or of the claustrum. 

The Corpora Quadrigemina, two on each side, are prominences 
on the dorsal surface of the pons and crura above the aqueduct 
of Sylvius. They contain white and gray matter. The pos- 
terior tubercles are connected with the eighth nerve, the sen- 
sory tract, the temporal region of the brain, and the lateral cor- 
pora geniculata. The anterior tubercles are connected with the 
optic nerve, with the occipital region, and with the median cor- 
pora geniculata. 

The function of the anterior of these bodies is mainly con- 
nected with the eye ; the posterior are associated with the sense 
of hearing. 

The Cerebrum. 

The great size of the cerebral hemispheres in man obscures 
the fact that the different parts of the brain are disposed in a 
linear series ; these, from before backward, are, the olfactory 
lobes, cerebral hemispheres, optic thalami, corpora quadrigem- 
ina, cerebellum, medulla oblongata. This arrangement exists 
in the human fetus, and persists throughout life in some of the 
lower animals. 



THE CEREBRUM. 



329 



Anatomy. — The substance of each hemisphere is divided by fis- 
sures into five lobes — {a) frontal, (£) parietal, (c) occipital, (d) 
temporo-sphcnoidal and (<?) central. The main fissures are four 
in number — (1 ) The fissure of Sylvius running from the front and 

Fig.|78." 




Left Side of the Human Brain (Diagrammatic). 
F, frontal ; P, parietal ; O, occipital; T, temporo-sphenoidal lobe; S, fissure of Sylvius ; 
S', horizontal ; S", ascending ramus of S ; c, sulcus centralis, or fissure of Rolando; A, as- 
cending frontal, and B, ascending parietal convolution; F x , superior, F 2 , middle, and F 3 , 
inferior frontal convolutions; f lf superior, and f 2 , inferior, frontal fissures; f 3 , sulcus 
precentralis ; P, superior parietal lobule; P 2 , inferior parietal lobule, consisting of P 2 , su- 
pra-marginal gyrus, and P 2 ', angular gyrus; ip, sulcus interparietalis ; cm, termination of 
calloso-marginal fissure ; O, first; 2 , second; 3 , third occipital convolutions; fio, pari- 
etal-occipital fissure; o, transverse occipital fissure; <? 2 , inferior longitudinal occipital fis- 
sure; T x , first; T 2 , second; T 3 , third, temporo-sphenoidal convolutions; t u first; t 2 , sec- 
ond, temporo-sphenoidal fissures. (Landois.) 



330 THE NERVOUS SYSTEM. 

under part of the brain backward, outward and upward; (2) 
the fissure of Rolando running from the median line near the 
center of the longitudinal fissure forward, outward and down- 
ward ; (3) the parieto-occipital fissure, little of which is evi- 
dent upon the surface of the brain, but which appears on longi- 
tudinal section separating the occipital and parietal lobes ; (4) 
the calloso-marginal fissure, also evident only on the internal 
aspect of the hemisphere, parallel with and above the corpus 
callosum. (Figs. 78, 79.) 

(a) The frontal lobe is bounded internally by the longitudinal 
fissure, posteriorly by the fissure of Rolando and below by the 
fissure of Sylvius. On its surface are seen three convolutions, 
approximately parallel, called the superior, middle and infei'ior 
frontal convolutions, and occupying positions which their names 
indicate. In addition the posterior portion of this lobe is occu- 
pied by the ascending frontal, or the anterior central convolution, 
lying just in front of the Rolandic fissure. 

{$) The parietal lobe is bounded anteriorly by the fissure of 
Rolando, internally by the longitudinal fissure, posteriorly by 
the parieto-occipital fissure and below by the fissure of Syl- 
vius. Just behind the fissure of Rolando is the ascending pa- 
rietal, or posterior central convolution ; above, this is continu- 
ous with the upper parietal convolution, below which is the 
inferior parietal lobule separated from the preceding by the 
intra-parietal sulcus. This inferior parietal lobule winds around 
the posterior part of the fissure of Sylvius, and is divided into 
the supra-marginal convolution, embracing the short arm of this 
fissure, and the angular convolution connecting below with the 
temporal lobe. 

(V) The occipital lobe is situated posteriorly below the 
parieto-occipital fissure and external to the median fissure. It 
presents three convolutions, the superior, middle and in- 
ferior. 

(d) The temporo-sphenoidal lobe is below the fissure of Sylvius 



THE CEREBRUM. 



33 l 



in front of the occipital lobe. It likewise presents superior, 
middle and ////^r/e?/' convolutions. 

(e) The central lobe, or island of Reil, presents the gyrus forni- 
catus, a convolution curving around the corpus callosum ; the 
marginal convolution beyond the calloso-marginal fissure from 
the preceding and between it and the edge of the longitudinal 
fissure; the continuation of the parietooccipital fissure running 

Fig. 79. 




Median Aspect of the Right Hemisphere. 
CC, corpus callosum divided longitudinally; Gf, gyrus fornicatus ; H, gyrus hippocampi; 
h, sulcus hippocampi; TJ, uncinate gyrus; cm, calloso-marginal fissure; F, first frontal 
convolution; c, terminal portion of fissure of Rolando; A, ascending frontal ; B, ascending 
parietal convolution and paracentral lobule; P/, praecuneus or quadrate lobule; Oz, 
cuneus; Po, parietooccipital fissure ; o', transverse occipital fissure; oc, calcarine fissure; 
oc', superior; oc", inferior, ramus of the same; G, gyrus descendens ; T 4 , gyrus occipito- 
temporalis lateralis (lobulus fusiformis) ; T 5 , gyrus occipito-temporalis medialis (lobulus 
lingualis). {Landois.) 

downward and forward to meet the calcarine fissure, between 
which is the cuneus ; the internal aspect of the temporal lobe, 
the icncinate gyrus. 



332 THE NERVOUS SYSTEM. 

Structure. — The cerebral hemispheres are composed of white 
and gray matter, but here the gray matter is situated externally. 
To increase its amount, with economy of space, the gray matter 
is thrown into many convolutions, to some of which reference has 
been made. The sulci separating these convolutions have a 
depth in the average human brain of about one inch. The 
thickness of the gray matter of the cortex varies from -^ to \ 
in. , being thinnest in the occipital and thickest in the front pa- 
rietal region. 

The cells found in the superficial and deep portions of the 
gray matter are not uniform in size or shape. In a general way 
it may be said that they increase in size as the surface is left, 
but in addition to the comparatively large cells in the deep 
parts there are also numbers of small ones. Passing in the same 
direction there are found in succession small pyramidal, larger 
pyramidal, and irregular branching cells. 

Fibers from the Cerebrum. — Fibers pass from each cerebral 
hemisphere to (a) the spinal cord, (<£) the cerebellum, (V) the 
opposite cerebral hemisphere, and (d) different parts of the 
same hemisphere. 

(# ) Fibers converge from the anterior and middle (particularly 
the latter) parts of the cortex to pass by the corona radiata to 
the corpora striata, from which fibers are continued to the crusta, 
pons, pyramids of the meditlla and pyramidal tracts of the cord ; 
most of these pass down through the internal capsule to reach 
the corpora striata. From the same regions also some fibers 
pass directly through the internal capsule, without connection 
with the corpora striata, to be actually continuous themselves 
with fibers which, following the same course downward, are found 
in the pyramidal tracts of the cord. All fibers passing from 
these cortical areas mentioned through the internal capsule 
occupy the anterior two thirds of the posterior division of that 
tract. Furthermore, fibers from the posterior cortical area pass 
through the posterior one-third of the posterior division of the 



THE CEREBRUM. 



333 



internal capsule to the optic thalamus, from which fibers pass 
through the tegmentum to the pons and medulla and are continu- 
ous with fibers from the sensory tracts of the cord. The decus- 
sation of all these fibers has been mentioned. 

Fig. 80. 




i 



Schema of the Projection Fibers Within the Brain. {Starr.) 
Lateral view of the internal capsule ; A, tract from the frontal gyri to the pons nuclei, and 
so to the cerebellum; B, motor tract; C, sensory tract for touch (separated from B for the 
sake of clearness in the schema); D, visual tract; E, auditory tract; F, G, H, superior, 
middle, and inferior cerebellar peduncles ; J, fibers between the auditory nucleus and the in- 
ferior quadrigeminal body; K, motor decussation in the bulb; Vt, fourth ventricle. The 
numerals refer to the cranial nerves. The sensory radiations are seen to be massed toward 
the occipital end of the hemisphere. (Am. Text-Book.) 

Fig. 8 1 taken in conjunction with Fig. 74 illustrates the most 
recent ideas of the motor and sensory connections between brain 
and cord and the motor and sensory paths in the cord. 

(£) Fibers from the anterior portion of the frontal lobe pass 
through the anterior limb of the internal capsule and seem to 
end in the gray matter of the pons and there to communicate with 
the cerebellum through the middle peduncles. Fibers also pass 
from the temporo-sphenoidal lobes and from the caudate nuclei 



Fig. 8i. 



a.c.n 




Multipolar 

Ceil of Ant 

Horn 



Skin 



Scheme of Relationship of Cells and Fibers of Brain and Cord. (Kirkes.) 

Pyr, cell of Rolandic area ; Ax, its axis cylinder crossing the middle line AB, to enter 
one of the pyramidal tracts ; the collateral Call goes to the cortex of the opposite hemis- 
phere, while another, str, enters the corpus striatum. The axis cylinder arborizes around an 
anterior horn cell, whence a motor fiber goes to the muscle. 

The axis cylinder from the spinal ganglion cell is represented as bifurcating and sending 
one branch to the periphery and one to the cord ; the latter itself bifurcates, the lower di- 
vision ending as shown better in Fig. 74. N.G, cell in posterior cornu of the cord or pos- 
terior column of the bulb. The distance of this cell from the point of entrance of the axis 
cylinder into the cord may be great or small. Note the collaterals from it in Fig. 74. LA, 
decussating fiber ending at cell in optic thalamus, O.T, from which a fiber passes to the 
cortex. A collateral is shown passing from the ascending sensory fiber to a cell of Clarke's 
column, whence a fiber passes to a cell, P, of the cerebellum. 



THE CEREBRUM. 



335 



of the corpora striata to the cerebellum on the opposite side. 
The connection is crossed in all these cases. 

(V) Transverse fibers in the corpus callosum connect all parts of 
the two lateral hemispheres. Besides these commissural fibers 
there are those of the anterior and posterior white commissures. 
Fibers in the anterior connect the temporo-sphenoidal lobes and 
probably the corpora striata with each other ; fibers in the pos- 
terior connect the temporo-sphenoidal lobes with the optic thalami 
of the opposite side. 

(d) The arcuate fibers connect different convolutions of the 
same lobe and the convolutions of different lobes with each 



Fig. 82. 




Diagram of the Motor Areas on the Outer Surface of a Monkey's Brain. 
dois after Horsley and Schafer.) 



(Lan- 



other. Some of these are in the fornix, in the corpus callosum, 
and in other parts, as well as running along the concave surface 
of the cortex. 

Cerebral Localization. — There are certain cortical areas which 
have certain fixed functions. There are certainly such areas for 
motion and for the reception of impressions conveyed by the 
nerves of special sense ; areas for the reception of impressions 
conveyed by the nerves of general sensatio?i have not been 
definitely determined. 



33 6 



THE NERVOUS SYSTEM. 
FIG. S 3 . 




Side View of the Brain of Man, with the Areas of the Cerebral Convolutions 
According to Ferrier. {Brubaker.) 

The figures are constructed by marking- on the brain of man, in their respective situa- 
tions, the areas of the brain of the monkey as determined by experiment, and the description 
of the effects of stimulating the various areas refers to the brain of the monkey. 

i, advance of the opposite hind limb, as in walking; 2, 3, 4, complex movements of the 
opposite leg and arm, and of the trunk, as in swimming; a, b, c, d, individual and com- 
bined movements of the fingers and wrist of the opposite hand. Prehensile movements. 5, 
extension forward of the opposite arm and hand ; supination and flexion of the opposite fore- 
arm ; 7, retraction and elevation of the opposite angle of the mouth by means of the zygomatic 
muscle ; 8, elevation of the alse nasi and upper lip, with depression of the lower lip on the 
opposite side; 9, 10, opening of the mouth, with (9) protrusion and (10) retraction of the 
tongue; region of aphasia, bilateral action ; 11, retraction of the opposite angle of the 
mouth, the head turned slightly to one side; 12, the eyes open widely, the pupils dilate, and 
the head and eyes turn toward the opposite side; 13, 13', the eyes move toward the opposite 
side, with an upward (13) or downward (i3')|deviation ; the pupils are generally contracted ; 
14, pricking of the opposite ear, the head and eyes turn to the opposite side, and the pupils 
dilate widely. 



THE CEREBRUM. 337 

Motor Centers. — Electrical stimulation of the convex surface 
of the cerebrum shows that the anterior part is motor and the 
posterior part non-motor; that stimulation of the motor por- 
tion produces muscular contractions on the opposite side of 
the body ; that stimulation in the same spot is always fol- 
lowed by the same contractions ; and that when the current is 
quite weak the contractions are limited to distinct muscles 
or sets of muscles. It may be further said that while ex- 
periments establishing these facts have been largely limited to 
inferior animals, the deductions have been made applicable to 
man by pathological observations and by the fact that in dif- 
ferent animals stimulation of anatomically corresponding parts 
is followed by corresponding results. Destruction of motor 
areas is followed by descending secondary degeneration of 
fibers through the corona radiata, internal capsule, crura cerebri 
(crust a), a?iterior pyramids of the medulla and the pyramidal 
tracts of the cord ; the resulting paralysis is on the- side opposite 
the lesion. 

The motor cortical zone, so far as can now be said, corre- 
sponds to the ascending frontal and parietal convolutions on 
either side of the fissure of Rolando, to the paracentral lobule, 
and possibly to a small area in front of the ascending frontal 
convolution. From above downward, on either side of the 
Rolandic fissure are areas presiding over the movements of the 
leg, arm and face. 

More specific information as regards areas controlling various 
movements may be obtained by reference to Fig. 83. 

Various kinds of monoplegia (crossed) are caused by lesions, 
as hemorrhage, in localized parts of the motor area \ there may 
be facial, brachial, crural, brachio -facial monoplegia, etc. There 
can be no doubt that from the motor cortical zone pass the fibers 
which constitute the pyramidal tracts of the cord. 

Sensory Centers. — Centers for the reception of impressions 
giving rise to general sensation may exist. Fibers from the tern- 



338 THE NERVOUS SYSTEM. 

poro-sphenoidal and occipital lobes pass through the posterior 
third of the posterior division of the internal capsule, and it 
may, therefore, be assumed that these parts of the cerebrum are 
connected with general sensation. 

Special Centers. — Besides these areas for motion and general 
sensation, special centers certainly exist. 

The Optic Center is in the occipital lobe, probably in the 
cuneus. Removal of the right occipital lobe is followed by left 
hemiopia and vice versa ; removal of both causes total blind- 
ness. 

The Olfactory Center is probably on the inner surface of the 
anterior extremity of the zmcinate gyrus (inner extremity of the 
temporal lobe^. 

The Gustatory Center is supposed to be in the temporal lobe 
very near the preceding. 

The Auditory Center is located in the superior and middle 
convolutions of the temporo-sphenoidal lobe. 

The Center for Cutaneous Sensations cannot be strictly lim- 
ited, though it is said to correspond with the motor area. 

The Center for Muscular Sensations is thought to be in the 
lower parietal region. 

The Speech Center. — One may not be able to speak because 
he cannot control the muscles usually involved in such an act, 
or because he has no comprehension of the meaning of words, 
or because he is incapable of forming the idea which links the 
reception of the impression and the muscular act. Aphasia is 
the term generally applied to inability to express one's self by 
language. It is to be distinguished, however, from aphonia, 
which is simply a loss of voice. Ataxic aphasia is an inability 
to express ideas only by reason of muscular incoordination ; a 
person so affected may use words, but he cannot tell what sounds 
he is going to utter ; his ability to receive ideas is unimpaired, 
and he can express his own ideas in writing. When there is 
inability to express ideas in writing, because of muscular inco- 



THE CEREBRUM. 339 

ordination, a condition of agraphic aphasia is said to exist. There 
are also cases in which a person can not comprehend ideas ex- 
pressed in language and cannot express himself by either speak- 
ing or writing; this is known as- amnesic aphasia. It is not 
impossible that in some instances ideas may be received and 
there still be an inability to express one's self in any way. It is 
noted that when the hemiplegia accompanying the aphasia is 
marked the form is usually ataxic ; when there is no hemiplegia 
the aphasia is usually amnesic. 

The part of the brain presiding over speech is in the left third 
frontal convolution near the island of Reil. In left-handed per- 
sons its usual situation is almost certainly at a corresponding 
point on the right side. Why the center is unilateral has not 
been explained. It may be that it was originally bilateral, 
and the growth of the right has been stopped by the superior 
development of the left side of the brain. It is at least noticed 
that the right instead of the left side of the brain is heavier 
in left-handed persons. Fibers from this center (Broca's con- 
volution) pass through the anterior part of the posterior divi- 
sion of the internal capsule to reach the left crus, leaving which 
they enter the pons to decussate and go to the right side of the 
medulla. 

Functions of the Cerebrum. — The superior development of 
the intellect in man is the most predominant characteristic dis- 
tinguishing him from the lower animals. That many such ani- 
mals are possessed of a certain degree of intelligence is not usu- 
ally denied ; and the nature of their mental operations, though 
they are insignificant as compared with man's, may be admitted 
as identical with his. The most striking difference in the nerv- 
ous system of man as compared with that of inferior animals 
is the large size of the cerebrum in the former. This is not 
surprising when it is admitted that in the substance of this part 
of the encephalon is the seat of those faculties which manifest 
themselves in mental operations. 



1 



34-0 THE NERVOUS SYSTEM. 

The seat of the changes, if they be changes, which result in 
mental operations is supposed to be in the frontal 'lobes ; these 
are insensible and inexcitable, but severe injury to them, as by 
hemorrhage, is followed by a cessation of mental activity ; con- 
genital defects also cause a corresponding decrease in the mental 
caliber. 

From what has been said it is evident that the cerebral hemis- 
pheres are capable of generating motor impulses a?id receiving im- 
pressions general and special ; but predominating in importance 
over these functions is the fact that the gray substance of the 
cerebrum is essential to the exercise of the intellect — even to the 
existence of that indefinite something called the mind. 

It is by the cerebrum that we perceive and retain impressions, 
that we understand, imagine, reflect, reason and judge, and thus 
concoct and issue the mandates of our will. It is the link which 
connects our impressions and our purposeful actions. 

In animals upon which experiments have been made it is 
found that life may persist for a time after the removal of the 
hemispheres, and that, outside of the cessation of mental activ- 
ity, the results are not so marked as one would on first thought 
suppose. Stupor and absence of the ordinary instinctive acts (as 
corresponding in a way with acts of the will in man) are noted, 
but voluntary motion and general sensibility are not destroyed, and 
may be but little interfered with. Of course there is no volun- 
tary motion in the sense of carrying out the behests of the will, 
for the organ of the will is destroyed ; nor is there any record of 
painful impressions, for the organ of memory is absent. But the 
animal can perform various consecutive and coordinate move- 
ments, such as walking, swimming, etc. For example, a pigeon 
thus mutilated will fly when thrown into the air. This does not 
argue any mental operation. A person does not ordinarily 
apply his mind to the act of walking or standing ; his mental 
faculties may be as completely engaged with the deepest thoughts 
of psychology, literature, medicine or other subjects while walk- 



THE CEREBRUM. 34 1 

ing as at any other time. True, he probably started with some 
fixed purpose to go in some particular direction to some definite 
place, but the act of progression does not per se require fixed at- 
tention on his part. So in the case of the pigeon ; it does not, 
make up its mind to fly at all ; and it will not fly without being 
thrown into the air, or the application of some other similar 
stimulus ; nor does it fly in any particular direction, or to any 
particular place. It is reduced to the condition of a "mechan- 
ism without spontaneity." It can perform voluntary move- 
ments, but cannot originate them without external intervention. 

Animals which have been subjected to the operation men- 
tioned undoubtedly feel pain. They move away or cry out on 
being burned, for example. The coordination of their move- 
ments and the cries contrast with the phenomena (reflex) fol- 
lowing such stimulation when only the cord is left. It was 
noted above that impressions in these cases are probably re- 
ceived by the gray matter of the pons and not recorded. 

The special senses of sight and hearing remain after the re- 
moval of the cerebrum. The same is probably true of taste and 
smell. 

It would seem that the cerebrum is a kind of storehouse in 
which are kept all the materials necessary for the performance 
of all kinds of pre-determined acts, whether they manifest 
themselves in speech, or thought, or muscular action. What 
excites these materials to activity — /. e., what excites a voluntary 
act — is not clear. We know certain things will usually excite 
a certain train of thought, or cause us to will to do or say cer- 
tain things. Such phenomena are akin to, if not identical with, 
reflex action. These manifestations of our voluntary power are 
due to impressions conveyed by afferent fibers to the cortex ; 
indeed it may be that every afferent fiber in the system exerts 
an influence thus indirectly upon the organ of the will, and the 
impressions conveyed by them are reflected in one's character 
and life. But it cannot be said that all voluntary activity is 



342 THE NERVOUS SYSTEM. 

thus of a reflected nature ; there is some cause other than the 

reception of afferent impressions which sets the will in operation. 

Connection Between the Brain and Intelligence. — It is 

claimed that a single hemisphere is capable of performing all the 
ordinary intellectual acts as well as both ; and atrophy, or de- 
struction otherwise, of one hemisphere has frequently been no- 
ticed to entail no mental defect. But whether the mind under 
such conditions would be equal to the highest intellectual 
attainments is doubtful. It would seem that in health the brain 
unites the impressions received by the two sides (as, e. g., through 
the optic nerves), and the resulting idea is a single one ; that is to 
say, a person does not have two opposing ideas about the same 
thing at the same time ; the two hemispheres seem to agree. 

In a general way, it may be stated that the degree of in- 
telligence corresponds to the weight of the brain, though to this 
rule there are many exceptions. It may be more properly said 
that the development of the intellectual faculties is greater as 
the area of gray matter is increased by the convolutions of the 
cortex. Idiots' brains are usually, though not by any means 
invariably, much below the average weight. 

A difference in intellectual vigor may be present in persons 
whose brains have the same weight and even the same amount of 
gray matter. A difference in the quality of the gray substance 
may in such cases account for the varying results. It is a matter 
of common observation that mental exercise increases mental 
vigor and capacity, just as muscular exercise develops muscular 
strength. It is difficult to reach a conclusion as to whether 
there is an increase in the amount of gray substance or whether 
that already present is endowed with additional power. 

The Cerebellum. 
Anatomy. — The cerebellum, or little brain (see Fig. 76), is 
situated beneath the occipital lobes of the cerebrum, weighs 
some 5^ ounces in the male to 4^ ounces in the female, and 



THe CEREBELLUM. 343 

consists of a central and two lateral lobes. It is composed of 
white and gray matter, the latter being, with the exception of 
the corpora dentata in the lateral lobes, situated externally. 
The convolutions on its surface are much finer than are those on 
the cerebral surface. It is separated from the parts above by the 
tentorium cerebelli, a process of the dura mater. 

Fibers. — The fibers passing away from the cerebellum are col- 
lected into three bundles on each side, known as the superior, 
middle and inferior peduncles. The superior peduncle has a 
direction forward and upward to reach the crus and optic thala- 
mus ; fibers in it connect the cerebellum with the cerebrum. 
Certain of these decussate underneath the corpora quadrigemina 
with corresponding fibers from the opposite side, so that each 
side of the cerebellum is connected with both sides of the 
cerebrum. Attention has been called to fibers passing down 
from the cerebrum through the pons to the cerebellum. Fibers 
in the middle peduncle connect the two lateral halves of the cere- 
bellum through the pons. Fibers in the inferior peduncle are 
continuous below with fibers in the posterior columns of the cord 
through the restiform bodies of the medulla. 

Function. — The only characteristic phenomenon invariably fol- 
lowing removal of the cerebellum is an inability to coordinate the 
voluntary muscular movements. The foot, for example, can be 
raised, and the voluntary muscular act concerned in raising it 
may be as vigorous as ever, but the animal cannot so govern his 
movements as to know where he may put it down. Even the 
coordination necessary in standing is lost, and the maintenance 
of the equilibrium is very difficult, if not impossible. The so- 
called muscular sense is abolished, and, while the power to con- 
tract the muscles remains, the animal cannot contract them in a 
regular or coordinate manner. When it is remembered that well 
nigh every voluntary act requires concerted or consecutive mus- 
cular movements some idea is gotten of the helpless condition 
sequent upon such a lesion. If it be granted that there is a 



344 THE NERVOUS SYSTEM. 

center presiding over the coordination of the voluntary muscles, 
that center is in the cerebellum, and an animal deprived of this 
organ is as powerless, so far as this function is concerned, as a 
person is to see when the optic centers are destroyed. Its action 
is crossed. 

It has been noted already that lesions of the posterior white 
columns of the cord are followed by disturbances of coordination, 
and that the cerebellum is connected with these columns through 
the inferior peduncles and restiform bodies. Fibers in these 
columns serve only as anatomical connections by which the co- 
ordinating center communicates with the muscles whose move- 
ments it is to regulate, and of necessity any lesion of these fibers 
destroying that connection is followed by a loss of control of the 
center over the muscles. However, in degeneration of the pos- 
terior columns (locomotor ataxia) an effort at coordination can 
be made, so that progression is possible by the aid of fixed at- 
tention. It is possible also that the coordinating messages are 
carried in such cases by the motor fibers, though in an unsat- 
isfactory manner. 

It has been supposed that the cerebellum is in some way con- 
nected with the generative function ; and this much is probably 
true, though the evidence submitted is not sufficient to warrant 
the assumption that the cerebellum is the seat of the sexual in- 
stinct. 

THE CRANIAL NERVES. 

The cranial nerves, twelve in number on each side, take their 
origin from some part of the encephalon, pierce the dura mater 
and leave the skull by various openings. They have been num- 
bered from before backward in the order in which they pass 
through the dura mater. Their names, indicating something of 
their function, and corresponding to their numbers, are as fol- 
lows : 

I. Olfactory. 
II. Optic. 



THE CRANIAL NERVES. 345 

III. Motor Oculi Communis. 

IV. Patheticus (Trochlearis) . 
V. Trifacial (Trigeminus). 

VI. Abducens. 
VII. Facial. 
VIII. Auditory. 
IX. Glossopharyngeal. 
X. Pneumogastric (Vagus). 
XL Spinal Accessory. 
XII. Hypoglossal. 

The point at which one of these nerves can be seen to issue 
from the brain tissue is the apparent origin, while the gray nu- 
cleus, or nuclei, to which the fibers can be traced in the brain 
substance is the deep origin. 

First Nerve (Olfactory). 

Origin. — This is a nerve of special sense. Its apparent origin 
is by three roots. The internal root issues from the gyrus forni- 
catus \ the middle from the under surface of the frontal lobe 
anterior to the anterior perforated space ; the external from the 
temporo- sphenoidal lobe. These three roots unite to pass for- 
ward underneath the frontal lobe near the longitudinal fissure 
as the olfactory tract. The deep origin is unsettled. 

Course and Distribution. — Reaching the upper surface of the 
cribriform plate of the ethmoid, the olfactory tract expands into 
the olfactory bulb, from the under surface of which are given 
off the special nerve fibers of the sense of smell. They are 
about twenty in number and pass through the foramina in the 
cribriform plate to be distributed to the mucous membrane 
(Schneiderian) of the nose in three sets — an inner to the upper 
third of the septum, a middle to the roof of the nares, and an 
outer to the superior and middle turbinated bones and the eth- 
moid in front of them. The fibers are non-medullated. 

Function. — The olfactory nerves are insensible and inexcit- 



346 THE NERVOUS SYSTEM. 

able. They are concerned with the sense of smell alone, and 
their integrity is necessary to the preservation of that sense. 
They convey to the brain impressions which are recognized as 
odors only. Removal of the olfactory bulb in a dog is evidently 
followed by a loss of the sense so characteristic of the animal. 
Furthermore, the olfactory bulbs in lower animals are shown to 
be developed in proportion to the acutenesss of the sense of 
smell. 

Second Nerve (Optic). 

Origin. — This is the nerve of sight. Its apparent origin is 
from the anterior part of the optic commissure. The optic com- 
missure occupies the optic groove on the superior surface of the 
sphenoid. It represents the union of the two optic tracts each 
of which, traced backward, is found to divide into two bands ; 
the extenial takes its origin from the external geniculate body, 
from the pulvinar of the optic thalamus and from the superior 
corpus quadrigeminum \ the internal comes from the internal 
geniculate body. These two, uniting, cross the crusta obliquely 
to reach the optic commissure, or chiasm. In the commissure 
the fibers from the inner margin of each optic tract pass to the 
other side of the brain, and may be called commissural fibers 
between the internal geniculate bodies. Some fibers anteriorly 
connect the two optic nerves with each other and are not prop- 
erly part of the chiasm, but connect the two retinae. The outer 
fibers of each tract pass to the nerve of the same side, while the 
central fibers decussate in the commissure with similar fibers 
from the other tract and pass thus to the optic nerve of the op- 
posite side. The deep origin is indicated above. 

Course and Distribution. — Each optic nerve leaves the 
front of the optic chiasm to pass out of the cranium and en- 
ter the orbital cavity by the optic foramen. Having pierced 
the sclerotic and choroid coats of the ball it expands into the 
retina. 

Function. — The optic nerves have no properties other than the 



THE CRANIAL NERVES. 347 

conveying to the brain of the special impressions of sight. 
Stimulation produces neither pain nor motion. 

Third Nerve (Motor Oculi Communis). 

Origin. — The third is a motor nerve. Its apparent origin is 
from the inner surface of the crus just in front of the pons Va- 
rolii. Its deep origin is in a nucleus just lateral to the median 
line beneath the aqueduct of Sylvius. Here decussation with 
fibers from the opposite side occurs. The fibers pass forward 
from this place through the locus niger and tegmentum to the 
point of apparent origin. 

Course and Distribution. — Having traversed the outer aspect 
of the cavernous sinus, the third nerve divides into two branches 
which leave the cranial cavity by the sphenoidal fissure between 
the two heads of the external rectus muscle of the eye. The 
superior division is distributed to the superior rectus and leva- 
tor palpebral superioris ; the inferior separates into three 
branches, one of which is distributed to the inferior rectus, 
another to the internal rectus, and a third to the inferior 
oblique. From this last a branch is given off to the lenticular 
ganglion to form its inferior root. 

Functions. — This nerve has no function other than to supply 
motion to the parts to which it is distributed. It is in- 
sensible at its root, but receives filaments from the fifth 
in the cavernous sinus, beyond which point stimulation pro- 
duces pain as well as muscular contractions. The phenom- 
ena sequent upon section of the nerve are suggested in its 
distribution, (i) There is ptosis, or dropping of the upper lid ; 
for the lid is kept open by the levator palpebrse superioris. (2) 
There is external strabismus, because the external rectus is not 
supplied by this nerve and is unopposed by the internal rectus, 
the action of which is paralyzed. Diplopia is the conse- 
quence. (3) There is inability to turn the ball except in an out- 
ward direction because the muscles producing movements on 



34-8 THE NERVOUS SYSTEM. 

the vertical and horizontal axes are deprived of innervation. 
(4) There is inability to rotate the eye in certain directions on 
the antero-posterior axis. The antagonist of the inferior obli- 
que is the superior oblique, the tendency of which latter is to 
rotate the globe so as to make the pupil look downward and 
outward. When the inferior oblique is paralyzed the superior 
oblique is unopposed, it is impossible to rotate the ball as is 
usual in sidewise movements. of the head, and double visionis the 
result. (5) There is slight protrusion of the whole ball from re- 
laxation of the muscles. (6) The pupil is dilated and move- 
ments of the iris are interfered with. Stimulation of the third 
nerve contracts the pupil, but when it is cut the pupil does not 
respond to light. The ciliary nerves controlling the movements 
of the iris come from the ophthalmic ganglion of the sympa- 
thetic ; to this ganglion goes a branch from the third nerve. It is 
known that the action of the sympathetic cannot be divorced 
from that of the cerebrospinal system; and whether this influ- 
ence of the third nerve is exerted directly upon the iris or in- 
directly through the ophthalmic ganglion is a matter of some 
obscurity. The fact that the action of the iris is not instanta- 
neous strongly suggests control by the sympathetic. 

The decussation under the aqueduct of Sylvius is evidenced by 
the reflex contraction of the pupil on the opposite side when the 
central end of a divided optic nerve is stimulated. The impulse 
is reflected through the third nerve. It is not to be understood, 
however, that the motor oculi is the only nerve capable of influ- 
encing movements of the iris. Section of the sympathetic in 
the neck contracts the pupil, even after section of the third. 

Fourth Nerve (Patheticus). 

Origin. — This is a purely motor nerve. Its apparent origin 

is behind the corpora quadrigemina from the valve of Vieussens. 

The two nerves decussate above this valve. Its deep origin is 

just below that of the third nerve beneath the aqueduct of Sylvius. 



THE CRANIAL NERVES. ^349 

Course and Distribution. — Emerging from the valve of Vie- 
ussens the nerve winds around the superior peduncle of the cere- 
bellum and the crusta immediately above the pons, and passes 
forward near the outer wall of the cavernous sinus to find exit 
from the cranial cavity by the sphenoidal fissure. Having en- 
tered the orbit, it runs forward to be distributed to the orbital 
surface of the superior oblique. In the cavernous sinus it 
receives fibers from the ophthalmic division of the fifth and from 
the sympathetic, and occasionally gives off a branch to the lach- 
rymal nerve. 

Function. — It supplies motor power to the superior oblique 
muscle alone. Remembering the origin and attachment of this 
muscle it is not difficult to foretell the consequence of lesions 
of the nerve. The action of the superior oblique is to rotate 
the ball upon an oblique horizontal axis so that the pupil will 
look downward and outward. This movement cannot be accom- 
plished when the nerve is cut, and the inferior oblique asserts 
itself unduly to bring about an opposite effect. The ball can- 
not accommodate itself to movements of the head toward the 
shoulder, and double vision supervenes — unless the object be 
brought in the involuntary line of vision of the affected eye. 

Fifth Nerve (Trifacial, Trigeminus). 

The fifth is analogous to the spinal nerves ( i ) in rising by two 
roots, (2) in having a ganglion on its posterior root, and (3) in 
having a mixed function. The anterior root is small and motor ; 
the posterior large and sensory. 

Origin. — Its apparent origin is from the side of the pons above 
the median line. The deep origin of the large, sensory root is in 
the pons immediately below the floor of the fourth ventricle and 
just internal to its marginal boundary. The small, motor root 
rises from a point just internal to the large root. 

Course and Distribution. — The two roots, taking their origin 
as above described, pass through the dura just above the internal 



350 THE NERVOUS SYSTEM. 

auditory meatus and run along the superior border of the petrous 
portion of the temporal bone to a point near its apex, where a 
large ganglion, the semilunar or Gasserian, is developed on the 
posterior root and occupies a depression on the bone for its re- 
ception. The motor root passes beneath the ganglion without 
being connected with it. 

The posterior root will be first followed to its distribution. 

From the anterior surface of the Gasserian ganglion are given 
off three branches — (i) ophthalmic, (2) superior maxillary, 
(3) inferior maxillary. After the inferior maxillary has left 
the cranial cavity it receives fibers from the small or motor root, 
but the other branches are composed entirely of fibers from the 
sensory root. 

1. The Ophthalmic Branch passes forward along the outer 
wall of the cavernous sinus, divides into three branches — (a) 
lachrymal, (ff) frontal, (7) nasal — and enters the orbit by 
the sphenoidal fissure. It communicates with the cavernous 
sympathetic, third and sixth nerves, (a) The lachrymal 
branch, running along the outer wall of the orbit, reaches the 
lachrymal gland, gives off filaments to it and to the conjunctiva, 
and pierces the tarsal ligament to be finally distributed to the 
integument of the upper lid. (£) The frontal branch runs 
along the upper wall of the orbit and separates into the supra- 
trochlear and supra-orbital branches. The former of these leaves 
the orbit in front and turns up over the bone to supply the in- 
tegument of the lower forehead ; the latter traverses the supra- 
orbital canal, escapes by the foramen of the same name, and 
supplies the skin as far back as the occiput as well as the peri- 
cranium in the frontal and parietal regions. (V) The nasal 
branch, crossing to the inner wall of the orbit, enters the anterior 
ethmoidal foramen, passes thus into the cranium again, runs in a 
groove on the cribriform plate of the ethmoid and finds exit into 
the nose through a slit by the side of the crista galli. Here it 
gives off branches which supply common sensation to the mucous 



THE CRANIAL NERVES. . 35 1 

membrane of the fore part of the nose, and then running in a 
groove on the posterior surface of the nasal bone, it leaves the 
cavity at the lower border of that bone to supply the integument 
of the ala and tip of the nose. From the nasal nerve pass fibers 
to the ophthalmic ganglion and to the ciliary muscle, iris and 
cornea. 

2. The Superior Maxillary Branch passes away from the 
Gasserian ganglion and leaves the cranium by the foramen ro- 
tundum. Crossing the spheno-maxillary fossa it enters the orbit 
through the spheno-maxillary fissure and traverses the infra- 
orbital canal to emerge upon the face at the infra-orbital foramen. 
In the cranium it gives off a meningeal branch to supply the 
neighboring dura mater. In the spheno-maxillary fossa it sup- 
plies branches {a) to the integument over the temporal and 
post-frontal regions and over the cheeks ; (b~) to the spheno- 
palatine ganglion ; (V) the posterior superior dental branches 
(generally two), which enter the posterior dental canals in the 
zygomatic fossa, and, passing forward in the substance of the 
superior maxilla, give off twigs to the fangs of the molar teeth, 
supplying them with sensation. In the infraorbital canal the 
superior maxillary nerve gives off (a) the middle superior den- 
tal, which runs downward and forward in the outer wall of the 
antrum to reach the roots of the bicuspid teeth ; (<£) the ante- 
rior superior dental, which likewise runs in the outer wall of the 
antrum to supply the incisor and canine teeth. After its exit 
from the infraorbital canal the nerve divides into palpebral, 
nasal and labial branches, which supply sensation to the regions 
indicated by their names. 

3. The Inferior Maxillary Branch after its exit from the 
cranium is a mixed nerve, supplying motion to the muscles of 
mastication as well as common sensation to the parts presently 
to be noted, and special sense to a part of the tongue. Its 
large or sensory root comes from the Gasserian ganglion to be 
joined just beneath the base of the skull by the small motor root 



352 THE NERVOUS SYSTEM. 

which has passed under the ganglion. Almost immediately 
this common trunk divides into (a) anterior and (/;) posterior 
branches, but first gives off a recurrent meningeal branch and a 
branch to the internal pterygoid muscle. 

(# ) The anterior of the two divisions of the inferior maxillary 
nerve receives nearly the whole of the motor root and divides 
into branches which supply the muscles of mastication, except- 
ing the internal pterygoid and the buccinator. 

(<£) The posterior division, chiefly sensory, divides into the 
auriculo-temporal, lingual and inferior dental branches. The 
auriculo-temporal branch runs backward to a point internal to 
the neck of the condyle of the inferior maxilla, then passing 
upward under the parotid gland divides into branches, which are 
distributed to the external auditory meatus, parotid gland, integ- 
ument of the temporal region and of the ear and surrounding 
parts. It communicates with the otic ganglion. The lingual 
branch is joined by the chorda tympani, passes to the inner side 
of the ramus of the jaw, crosses Wharton's duct, and is distrib- 
uted to the papillae and mucous membrane of the tongue and 
mouth. It communicates with the facial through the chorda 
tympani, with the hypoglossal, and with the submaxillary gan- 
glion. The inferior dental branch passes between the internal 
lateral ligament and ramus of the jaw to enter the inferior dental 
foramen. Thence it traverses the dental canal in the inferior 
maxilla to issue at the mental foramen. Here it divides into 
incisor and mental branches \ the former continues in the bone 
to supply the incisor and canine teeth ; the latter supplies the 
skin of the chin and lower lip. In its course the inferior dental 
gives off the i?iylo-hyoid (before entering the canal) to the mylo- 
hyoid and anterior belly of the digastric, and dental brandies 
to supply the molar and bicuspid teeth. 

Four small ganglia, usually classed as part of the sympathetic 
system, are connected with the three divisions of the trifacial 
nerve. The ophthalmic, or lenticular, ganglion is connected 



THE CRANIAL NERVES. 353 

with the first division ■ the spheno-palatine or Meckel's with 
the second ; the otic and submaxillary with the third. All 
these receive sensory fibers from the trifacial and motor fibers 
from various sources. 

Functions. — It is seen from the foregoing description that 
the trifacial is the great sensory nerve of the head and face, and 
the motor nerve of the muscles of mastication. The small, or 
motor, division has properly been called the " nerve of mastica- 
tion. M It is insensible upon stimulation before it is joined by the 
third division of the sensory root. Its section causes paralysis 
of the muscles of mastication on that side. It cannot be doubted 
that the large root is exclusively sensory at its origin, and the 
acuteness of that sensibility, as, e. g., in the teeth, is a matter of 
common observation. Immediate loss of sensibility in the area 
of its distribution follows section, and even the cornea, which is 
normally exquisitely sensitive, can be touched without exciting 
pain. Both roots are usually cut at the same time, and besides 
a loss of motion and general sensibility, section of this nerve 
produces a decided effect upon the eye, the sense of taste, deglu- 
tition and the nutrition of the parts to which the nerve is 
distributed. The flow of tears is increased, the pupil be- 
comes temporarily contracted and the ball protrudes. In a 
few hours congestion is marked, and in a day or two the 
cornea sloughs and the eye is destroyed. Section of the fifth 
before its lingual branch is joined by the chorda tympani from 
the facial causes a loss of general sensation, but not of taste, in 
the anterior part of the tongue ; section of the lingual branch 
after it has received the chorda is followed by loss of general 
sensation and of taste. This shows that the special sensibility 
distributed to the tongue by the lingual branch of the fifth is 
furnished by the chorda tympani. The fifth nerve sends fila- 
ments to give sensibility to the velum palati. The reflex act 
of deglutition is due to impressions carried from the velum 
and neighboring parts to the centers ; when the fifth nerve is 
23 



354 THE NERVOUS SYSTEM. 

cut no such impressions are conveyed and the reflex act cannot 
be excited. 

Regarding nutrition it is noticed that, besides the sloughing of 
the cornea, there is also, about the same time, the appearance of 
ulcers in the mouth and on the tongue, and animals thus experi- 
mented upon soon die. These lesions are much less marked 
when the section is behind the semilunar ganglion. Explanations 
of this difference are not altogether satisfactory, but it is rational 
to suppose that section of sympathetic fibers when the nerve 
is cut in front of Gasser's ganglion is responsible for the dis- 
turbances of nutrition \ for this is the system of nutrition, and 
changes following its section in other parts of the body are not 
unlike those under discussion. Why, however, the changes 
should be inflammatory in character is not explained by this hy- 
pothesis, unless it be an explanation to say that the inflammation 
is set up by the impairment of nutrition in these structures — the 
impairment resulting in part from the impoverished condition of 
the blood as a consequence of the inability of the animal to chew. 

Sixth Nerve (Abducens). 

Origin. — This is a motor nerve entirely. Its apparent origin 
is from the lower border of the pons in the groove separating it 
from the anterior pyramid of the medulla. Its deep origin is 
close to the median line beneath the floor of the fourth ventricle 
a little below the motor root of the fifth. 

Course and Distribution. — The nerve enters the cavernous 
sinus, runs forward to enter the orbit by the sphenoidal fissure, 
passes between the two heads of the external rectus, and is dis- 
tributed to the ocular surface of that muscle. In the cavernous 
sinus it receives fibers from the first division of the fifth and from 
the sympathetic. 

Function. — The function is indicated in its distribution. It 
is insensible at its origin. Stimulation produces contraction of 
the external rectus ; section causes paralysis of that muscle and 
consequent internal sti'abismus and diplopia. 



THE CRANIAL NERVES. 355 

Seventh Nerve (Facial). 

Origin. — The apparent origin of the seventh is from the up- 
per end of the medulla in the groove between the olivary and 
restiform bodies. Its deep origin is in the pons beneath the 
floor of the fourth ventricle a little external to the nucleus of 
the sixth. 

Course and Distribution. — The seventh nerve passes outward 
and forward with the auditory nerve (on its inner side) to enter 
the internal auditory meatus. From their relative firmness and 
texture and their close relation here, the seventh and eighth 
nerves have been called respectively the portio dura and the 
portio mollis. Running between them is a fasciculus from the 
medulla known as the intermediary nerve of Wrisberg, or the 
portio inter duram et mollem ; most of its fibers join the 
facial in the internal auditory meatus. The facial nerve enters 
the Fallopian aqueduct at the bottom of the meatus and follows 
it to issue at the stylo-mastoid foramen, run forward in the sub- 
stance of the parotid gland and divide behind the ramus of the 
jaw into temporo -facial and cervico-facial branches. 

Its branches of communication are numerous, (i) In the in- 
ternal auditory meatus it communicates w r ith the auditory nerve ; 
(2) in the aqueductus Fallopii,'vt\i\\ the otic and spheno-palatine 
ganglia, with the sympathetic and with the auricular branch of 
the pneumogastric ; (3) after leaving the stylo-mastoid foramen, 
with the fifth, ninth, tenth and sympathetic. 

Its branches of distribution are also quite numerous. (1) In 
the aqueductus Fallopii it gives off (a) the tympanic branch to the 
stapedius muscle, and (<£) the chorda tympani, which passes 
through the cavity of the tympanum and emerges by a foramen at 
the inner end of the Glaserian fissure to go to the lingual branch 
of the fifth. ( 2 ) At its exit from the stylo-mastoid foramen it gives 
off {a) a posterior auricular branch which, receiving a filament 
from the auricular branch of the tenth, is distributed to the 



35 6 THE NERVOUS SYSTEM. 

retrahens aurem and the occipital portion of the occipitofron- 
tal ; (b) a digastric branch to the posterior belly of the di- 
gastric muscle; (V) a stylo-hyoid branch to the muscle of that 
name. (3) On the face it divides into (a) a temporo- facial 
branch, which is distributed to the muscles over the temple and 
upper face; and (/?) a cervicofacial branch, which is distributed 
to the lower face and upper cervical region. 

Functions. — This is the motor nerve of the muscles of ex- 
pression, of the platysma, buccinator, digastric (posterior belly), 
stylo-hyoid, the muscles of the external ear and the stapedius. 
Communicating freely with the fifth, it also contains sensory 
fibers, but it is in all probability insensible at its root. Its sec- 
tion causes paralysis of the muscles which it supplies, but no 
marked changes in sensation. The branches to the otic and 
spheno-palatine ganglia in the aqueductus Fallopii constitute 
their motor roots ; the branch given off in this situation to the 
tenth supplies it with motor filaments, and probably also here 
pass sensory fibers from the tenth to the seventh. In facial 
paralysis when the lesion is in the aqueductus Fallopii or behind 
it, there is paralysis also of the muscles of the palate and uvula, 
the uvula is drawn to the opposite side and there is trouble in 
deglutition. The fibers to the azygos uvulae and levator palati 
pass from the aqueductus Fallopii through Meckel's ganglion. 

The effect of paralysis of the facial upon the superficial muscles 
of the face is suggested in its distribution. The brow cannot be 
corrugated ; the eye is constantly open and there may be con- 
sequent inflammation from exposure ; the nostril cannot be di- 
lated, and inspiration and possibly olfaction are interfered with ; 
the cheek is flaccid ; the lips are immobile and saliva may flow 
from that corner of the mouth ; the buccinator is paralyzed, and 
there is often great difficulty in mastication because of the accu- 
mulation of food between the cheek and the teeth ; the unop- 
posed action of the muscles of the opposite side greatly distort 
the facial features, the affected side being quite expressionless. 



THE CRANIAL NERVES. 35 7 

Facial monoplegia is common ; facial diplegia is very uncommon. 
The Chorda Tympani. — This branch of the seventh is con- 
cerned especially in gustation. The fibers of which it is com- 
posed undoubtedly come from the nerve of Wrisberg. Section 
of the seventh involving also the nerve of Wrisberg causes not 
only facial palsy but also a loss of the sense of taste in the an- 
terior two-thirds of the tongue. The sense of taste will receive 
later notice. 

Eighth Nerve (Auditory). 

Origin. — This is a nerve of special sense. Its apparent origin 
is by two roots — one from the groove between the olivary and 
restiform bodies at the lower border of the pons, the other com- 
ing around the upper end of the restiform body to join the first 
in the groove. The deep origin of the two roots is different. 
That of the median root is the dorsal auditory nucleus in the 
floor of the fourth ventricle ; that of the lateral root is mainly 
from the ventral auditory nucleus in front of the restiform body 
between the two roots. 

Course and Distribution. — Crossing the posterior border of 
the middle peduncle of the cerebellum, it enters the internal audi" 
tory meatus in company with the facial nerve and the nerve of 
Wrisberg. At the bottom of the meatus it receives fibers from 
the seventh, and divides into branches which pass to the cochlea, 
semicircular canals and vestibule. 

Function. — This nerve receives and conveys to the brain im- 
pressions produced by sound waves ; it is the nerve of hearing 
and is in all probability not sensible to stimulation in any other 
way. 

Ninth Nerve (Glosso pharyngeal). 

Origin. — The apparent origin of this nerve is from the upper 
part of the medulla in the groove between the olivary and resti- 
form bodies. Its deep origin is in the lower part of the floor of 
the fourth ventricle above the nucleus of the tenth. 



358 THE NERVOUS SYSTEM. 

Course and Distribution. — Leaving the skull by the jugular 
foramen, it passes forward between the internal jugular vein and 
the internal carotid artery, descends in front of the latter to the 
lower border of the stylo-pharyngeus where it curves inward, 
runs beneath the hyoglossus, and is distributed to the fauces, 
posterior third of the tongue, and the tonsil. 

It communicates with the seventh, tenth and sympathetic. 

Its branches of distribution go to the mucous membrane and 
muscles of the pharynx, the stylo-pharyngeus, the tonsil and 
soft palate, the circumvallate papillae and the mucous membrane 
at the base and side of the tongue and on the anterior surface of 
the epiglottis. Some of its branches join branches from the 
pharyngeal and external laryngeal branches of the pneumogastric 
to form the pharyngeal plexus. 

Functions. — It is the nerve of sensation to the pharynx and 
fauces and a nerve of taste to the base of the tongue. Its sensi- 
bility at its root is dull, but stimulation produces no motion. 
Although this nerve is distributed to the mucous membrane over 
the base of the tongue, palate and pharynx, these parts receive 
the greater portion of their general sensibility from filaments of 
the fifth, and section of the ninth produces no marked effect 
upon the reflex phenomena of deglutition. The sense of taste is 
distributed to the anterior two-thirds of the tongue by the chorda 
tympani, and it has nothing to do with general sensation, while 
the glosso-pharyngeal, endowing the posterior third with gusta- 
tory power, also furnishes to it a degree of general sensibility. 

Tenth Nerve (Pneumogastric, Vagus). 

Origin. — This is a mixed nerve. Its apparent origin is from 
the groove between the olivary and restiform bodies below the 
ninth. Its deep origin is in the floor of the fourth ventricle 
just below that of the glosso-pharyngeal. 

Course and Distribution. — As it leaves the cranium by the 
jugular foramen it presents a ganglionic enlargement, the jugu- 



THE CRANIAL NERVES. 359 

lar ganglion, or ganglion of the root, just below which it is 
joined by the accessory portion of the spinal accessory. Below 
the junction is a second ganglion, the ganglion of the trunk. 
The accessory part of the eleventh passes through this ganglion, 
and below unites with the vagus trunk to pass chiefly into its 
pharyngeal and superior laryngeal branches. The pneumogas- 
tric passes down the neck behind and between the internal 
jugular vein and the internal and common carotid arteries, and 
sends motor and sensory fibers to the organs of voice and res- 
piration, and motor fibers to the pharynx, esophagus, stomach 
and heart. 

The branches of the pneumogastric are numerous, (i) In 
the jugular fossa it gives off (a) a meningeal branch to the dura 
mater of the posterior fossa of the skull ; (<£) an auricular 
branch which, traversing the substance of the temporal bone, 
emerges by the auricular fissure to supply the integument of the 
back part of the pinna and external auditory meatus. (2) In 
the neck it gives off (a) a pharyngeal branch, which consists 
mainly of fibers from the accessory portion of the eleventh and 
is the chief motor nerve of the pharynx and soft palate ; (<£) a 
superior laryngeal branch, which also consists mainly of fibers 
from the accessory part of the eleventh and is the chief sensory 
nerve of the larynx ; it also animates the crico-thyroid muscle ; 
(c) a recurrent laryngeal branch, which, on the right side, winds 
round the subclavian artery, and, on the left, round the aorta to 
return to the muscles of the larynx whose motor nerve it is ; (I) 
cervical cardiac branches, which communicate with the cardiac 
branches of the sympathetic and pass to the deep cardiac plexus. 
(3) I11 the thorax it gives off (a) thoracic cardiac branches, 
which pass to the deep cardiac plexus \ (b) anterior pulmonary 
branches, which go to the roots of the lungs in front ; (V) pos- 
terior pulmonary branches, which go to the roots of the lungs 
behind and send some filaments to the pericardium ; filaments 
from (b) and (V) follow the air passages through the lungs ; (a 7 ) 



360 THE NERVOUS SYSTEM. 

esophageal branches, which unite with fibers from the opposite 
nerve to form the esophageal plexus. (4) In the abdomen are 
the gastric branches ; those from the left nerve are distributed 
to the anterior surface of the stomach, and those from the right 
to the posterior \ the right vagus is also distributed to the liver, 
spleen, kidneys and entire small intestine. 

Throughout the whole course of the pneumogastric commu- 
nication with other nerves, especially the sympathetic, is very 
free. 

Functions. — The root of the tenth in the medulla is purely 
sensory, but the nerve communicates with at least five motor 
nerves, and is distributed to mucous membranes and to voluntary 
and involuntary muscle tissue. The auricular branches contain 
both motor and sensory fibers, and their function is indicated in 
their distribution. The pharyngeal branches are mixed, re- 
ceiving motor filaments from the spinal accessory. Sensibility 
is supplied to the pharynx not by this nerve alone, but by the 
branches of the fifth and probably of the ninth ; indeed it 
seems that the pharyngeal branches of the tenth have little to do 
with the reflex phenomena of deglutition. The superior laryn- 
geal branches, mainly sensory, supply also motor power to the 
crico-thyroids. Stimulation of the filaments of these branches 
prevents the entrance of foreign bodies into the larynx by reflex 
closure of the glottis, and also excites movements of deglutition. 
Their section produces hoarseness. The recurrent, or inferior 
laryngeal, branches, chiefly motor, supply the muscular tissue 
of the upper esophagus and trachea, as well as the muscles of the 
larynx. Section of them causes embarrassed phonation, though 
the fibers thus influencing the vocal sounds come to the recur- 
rent laryngeal from the spinal accessory. The uses of the car- 
diac branches have been noticed under discussion of the heart's 
action. The pulmonary branches are both motor and sensory 
and go to the lower trachea, the bronchi and lung substance. 
Section of the tenth destroys the sensibility of the mucous mem- 



THE CRANIAL NERVES. 361 

brane of the trachea and bronchi and the contractile power of 
the muscular fibers of the tubes. The esophageal branches are 
mixed, though motor fibers predominate. Food will not pass 
readily into the stomach on section of the tenth because of the 
absence of muscular contractions in the esophagus. 

Influence of the Vagus on Respiration, — Section of both 
these nerves temporarily increases the number of respirations, 
which soon, however, become exceedingly slow until death 
ensues. Inspiration is very profound — indeed so profound as to 
produce rupture of some of the pulmonary capillaries with con- 
sequent hemorrhage and coagulation of the blood and consolida- 
tion of the lung in part or whole. Section of only one of the vagi 
is not usually followed by death. Further notice of the relation 
of the pneumogastric to respiration is given elsewhere. 

Influence of the Vagus on the Stomach, Intestine and 
Liver. — Stimulation of the pneumogastric causes contraction of 
the stomach ; but, since the contraction is not immediate, the 
impulse is probably carried to it by fibers of the sympathetic 
running with the gastric branches of the tenth. When the 
vagus is cut during digestion in the stomach the contrac- 
tions of the muscular wall are impaired and the sensibility of 
the organ is abolished. Secretion is interfered with, but not 
stopped. 

Section of the vagus seems also to impair intestinal secretion 
and movements, but it is not improbable that this is because 
sympathetic fibers joining the vagus high in the neck are dis- 
tributed with it to the intestine. 

Simple division of the pneumogastrics inhibits the formation 
of glycogen in the liver ; but when the central ends of the cut 
nerves are stimulated there is an increased production of sugar 
even to the point of glycosuria. The irritation is probably re- 
flected through the sympathetic ; indeed it is not supposed that 
the vagi are concerned in the glycogenic function of the liver 
except reflexly ; its section only prevents the conduction 



362 THE NERVOUS SYSTEM. 

cephalad of the impressions which usually give rise to a secre- 
tion of glycogen. 

The connection of the vagus with the kidneys, spleen and 
suprarenal capsules is obscure. 

Eleventh Nerve (Spinal Accessory). 

Origin. — This nerve consists of a cranial portion, accessory 
to the tenth, and a spinal portion. The apparent origin of the 
cranial root is from the side of the medulla just below the vagus. 
Its deep origin is in the medulla to the posterior and outer side 
of the nucleus of the ninth. The apparent origin of the spinal 
portion is by several filaments from the side of the cord as low 
down as the sixth cervical nerve. Its deep origin is from a 
column of cells in the anterior cornu of gray matter of the cord. 

Course and Distribution {Accessory Portion). — Passing out to 
the jugular foramen it is joined by the spinal portion, and sends 
a few filaments to the ganglion of the root of the tenth \ then 
leaving the spinal portion it finds exit from the cranium by the 
jugular foramen, passes over the ganglion of the trunk of the 
tenth (adherent to it), and is continued chiefly in the pharyngeal 
and superior laryngeal branches of that nerve (Gray), but in the 
recurrent laryngeal as well. 

Spinal Portion. — Running upward between the two roots of 
the spinal nerves the spinal portion enters the cranial cavity by 
the foramen magnum, passes outward to the jugular foramen, 
where it joins the accessory portion to separate from it on pass- 
ing through that foramen. After leaving the skull it takes a 
course backward, pierces the sterno-mastoid, crosses the occipital 
triangle and terminates in the trapezius. It gives branches to 
the sterno-mastoid and to the cervical plexus. 

Functions. — Both roots of this nerve are purely motor, but 
communication with other nerves gives it a degree of sensi- 
bility. The fibers from the medulla (accessory) go exclusively 
to the muscles of the larynx and pharynx, while those from the 



THE CRANIAL NERVES. 363 

cord (spinal) go exclusively to the sterno-mastoid and trapezius ; 
and section of either root separately is followed by phenomena 
corresponding to these facts. When both roots are divided 
there is loss of voice, disturbance of deglutition, loss of cardiac 
inhibition and partial paralysis of the sterno-mastoid and tra- 
pezius. The loss of voice and disturbance in deglutition are 
explained by the distribution of the fibers of the eleventh with 
the pharyngeal and laryngeal branches of the tenth. The loss 
of the power of the vagus to inhibit cardiac action is because the 
fibers of the tenth which convey the inhibitory impulses are re- 
ceived from the spinal accessory. The sterno-mastoid and 
trapezius are only partially paralyzed because they receive motor 
fibers also from the cervical plexus. 

Twelfth Nerve (Hypoglossal). 

Origin. — This nerve supplies motion to the tongue. Its ap- 
parent origin is by 10-15 filaments in the groove between the 
anterior pyramid of the medulla and the olivary body. Its 
deep origin is in the floor of the fourth ventricle under the 
lower border of the fasciculus teres. 

Course and Distribution. — The nerve passes through the an- 
terior condyloid foramen in two bundles which unite to form a 
common trunk below. Running downward in company with 
the internal carotid artery and internal jugular vein, it reaches a 
point opposite the angle of the jaw, then runs forward, crosses 
the external carotid, lies on the hyoglossus and is continued for- 
ward in the genio-hyoglossus to the tip of the tongue. 

It communicates with the tenth, sympathetic, first and second 
cervical and the lingual branch of the fifth. 

Its branches of distribution are (1) meningeal to the dura 
mater in the posterior fossa of the skull; (2) descendens hypo- 
glossi, which, running downward across the sheath of the great 
vessels, meets branches of the second and third cervical nerves 
to form a loop from which are supplied the sterno-hyoid, the 



364 THE NERVOUS SYSTEM. 

omo-hyoid and the sterno-thyroid muscles ; (3) thyro-hyoid to 
the muscle of that name; (4) muscular to the muscular sub- 
stances of the tongue and to the styloglossus, hyoglossus, 
genio-hyoid and genio-hyoglossus muscles. 

Functions. — This nerve possesses no sensibility at its root, 
but receives sensory fibers from anastomoses with other nerves. 
Its stimulation, therefore, causes movements of the tongue and 
some pain. Section of both nerves causes difficult deglutition, 
loss of power over the tongue and consequent disturbances in 
mastication and articulation. When the twelfth is affected in 
hemiplegia the tongue, on protrusion, deviates to the affected 
side because it \s pushed out by the genio-hyoglossus. 

It will be seen from the foregoing that, classified according to 
their properties at their roots, the I., II. and VIII. are nerves 
of special sense; the III., IV., VI., XI. and XII. are motor; 
the X. is sensory; and the V., VII. and IX. are mixed. It is 
to be remembered, however, that most of these (excepting the 
nerves of special sense) are mixed in their distribution by reason 
of the reception of fibers from other nerves. The term ' ' mixed ' ' 
in the above classification is used as meaning the association of 
special sensory fibers with motor or common sensory fibers as 
well as the association of these latter with each other. The VII. 
is classed as a mixed nerve only by allowing that the intermediary 
nerve of Wrisberg is to be considered a part of it. Its own 
proper root is purely motor. 

THE SPINAL NERVES. 

The spinal nerves, thirty-one on each side, are so called from 
the fact that they originate in the spinal cord and escape from the 
spinal can.al by the intervertebral foramina. Eight pairs come 
from the cervical region of the column, twelve from the dorsal, 
five from the lumbar, five from the sacral, and one from the 
coccygeal. They are numbered according to their foramina of exit. 



THE SPINAL NERVES. 



36S 



Each nerve rises by two roots — an anterior which can be 
traced to the anterior cornu of gray matter and a posterior which 
goes (apparently) to the posterior cornu — and these emerge re- 
spectively from the antero -lateral and postero-lateral fissures of 
the cord. Before leaving the spinal canal these two roots join 
to pass through the corresponding intervertebral foramen as a 
single trunk which, however, just beyond that foramen divides 
into anterior and posterior branches to be distributed to the an- 
terior and posterior parts of the body. 

The posterior root (inside the spinal canal) is sensory, and 
has a ganglion developed upon it. The fibers of the posterior 
root are outgrowths of cells in the ganglion of that root, as indi- 
cated in Fig. 84. This accounts for the arborization of the dif- 

Fig. 84. 




A, bipolar cell from spinal ganglion of a 4^ weeks' embryo (after His), n, nucleus ; the 
arrors indicate the direction in which the nerve processes grow, one to the spinal cord, the 
other to the periphery. B, a cell from the spinal ganglion of the adult ; the two processes 
have coalesced to form a T-shaped junction. (Kirkes.) 

ferent fibers around cells in the cord instead of an actual connection 
with them. These facts should not be lost sight of though it is 
customary to speak of an afferent fiber as passing directly to a 



366 THE NERVOUS SYSTEM. 

cord cell itself. The anterior root is entirely motor except for 
a degree of " recurrent" sensibility which is due to the presence 
in it of posterior root fibers which have passed backward from 
the point of junction of the two probably to supply the mem- 
branes of the cord. The common trunk is, of course, mixed, as 
are the anterior and posterior branches passing from it. 

These spinal nerves are distributed to the muscles of the trunk 
and extremities, to the integument of almost the entire body 
and to some mucous membranes ; and from what has been said 
in speaking of the cord about the connection between it and 
these nerves, and their connection through it with the higher 
centers, it is evident that they are most important factors which, 
acting under the guidance of the sensorium, on the one hand, 
tell of the condition of the organism — its relations and environ- 
ments — and, on the other, control the voluntary movements of 
the body. 

The spinal nerve fibers come in part directly from the brain 
and in part from the gray cells of the cord. 

THE SYMPATHETIC SYSTEM. 

The sympathetic has been separated from the cerebro-spinal 
system only for the sake of convenience. The former sends 
filaments to the latter and receives both motor and sensory fibers 
in return, while the cooperation of the two systems, regulating 
in harmonyall the physiological processes going on in the body, 
is too evident to be questioned. 

The sympathetic system is remarkable for the number of 
ganglia connected with it. These may be divided into (a) 
those along the vertebral column, as the thoracic, (£) those in 
close proximity to the viscera and from which those viscera a're 
to be directly supplied, as the semilunar, and (c) terminal 
ganglia which the fibers reach just before final distribution, as 
the cardiac, intestinal, etc. The sympathetic is, therefore, fre- 
quently known as the ganglionic system. 



THE SYMPATHETIC SYSTEM. 367 

Arrangement. — There is on each side of the spinal column, 
extending from the lenticular ganglion above to the ganglion 
impar below, a chain of ganglia all of which are united to each 
other and to the ganglia of the opposite chain by commissural 
fibers. From these ganglia go fibers to form numerous plexuses 
and to be distributed to the various parts. In the skull there 
are four of these ganglia, the otic, ophthalmic, submaxillary 
and spheno-palatine or Meckel's ; in the cervical region there 
are three ; in the dorsal twelve ; in the lumbar four j in the 
sacral four or five ; and in front of the coccyx the single gang- 
lion impar. 

Connections between the cranial nerves and cranial sympa- 
thetic ganglia have already been noted. 

The cervical ganglia are of special interest as furnishing the 
chief sympathetic supply to the heart. 

The thoracic or dorsal ganglia give rise to the sympathetic 
supply for the great abdominal viscera. From the sixth, seventh, 
eighth and ninth springs the great splanchnic nerve, which 
passes through the diaphragm to the semilunar ganglion. This 
is the largest of the sympathetic ganglia, and is sometimes called 
the abdominal brain. It has been inaccurately called the center 
of the sympathetic system. The two ganglia occupy positions 
on opposite sides of the celiac axis, and give rise to fibers which 
supply most of the abdominal viscera. The tenth and eleventh 
thoracic ganglia give rise to the lesser splanchnic nerve. From 
the last thoracic springs the renal splanchnic nerve. The radi- 
ating fibers from the semilunar ganglia form the solar plexuses 
for the two sides. 

The lumbar ganglia give off fibers to form the aortic lumbar 
and hypogastric plexuses. 

The sacral and coccygeal ganglia supply the pelvic vessels. 

Properties. — The ganglia and nerves are slightly sensitive. 
Contraction of involuntary muscular tissue follows stimulation — 
not immediately, but after a considerable interval, and the sub- 



368 THE NERVOUS SYSTEM. 

sequent relaxation is tardy. Some of the ganglia are dependent 
for power upon their fibers from the cerebro-spinal system, while 
others seem capable of acting independently, at least for a time. 

Functions. — Little is known of the functions of the sympa- 
thetic except as regards its efferent fibers. They are distributed 
in general to the non-striped musculature of the circulatory appa- 
ratus and of the viscera, to secreting glands and to the heart. The 
heart furnishes the only example of a direct sympathetic supply 
to striated muscle. The sympathetic has a very definite effect 
upon secretion, nutrition and the local production of heat. Sec- 
tion of the sympathetic fibers going to any part causes hyper- 
emia, an increased amount of secretion (sweat, e. g.), and a rise 
of temperature in that part. The last two conditions are caused 
by the first, and it in turn is due to a paralysis of the muscular 
coat of the vessels, allowing an abrogation of their usual tonic 
condition and, consequently, dilatation and an increased amount 
of blood with exaggerated nutritive activity. This statement 
confronts us with the question of vaso-motor action. 

Vaso-motor Phenomena. — By vaso-motor nerves is meant 
those fibers which convey to the muscular coat of the vessel 
walls impulses causing them to contract and decrease the caliber, 
or to relax and increase it. Those causing contraction are called 
vaso-constrictors ; those causing relaxation vaso-dilators. It 
is mainly through the operation of vaso-motor nerves that the 
sympathetic system influences nutrition in a particular part, 
though all vaso-motor fibers are not confined to the sympathetic 
cords. However, it is not through the operation of the vaso- 
motor nerves alone that the sympathetic lays claim to be the 
"system of nutrition," for all the parts to which its other fibers 
are distributed contribute also very materially to nutrition, 
though perhaps in not so direct a manner as do the muscular 
coats of the arteries. While intestinal peristalsis, the secretion 
of many glands, as, for example, the production of glycogen, 
bile, etc., cannot be shown to be absolutely dependent on sym- 



THE SYMPATHETIC SYSTEM. 369 

pathetic connections, yet all these processes — nutritive in na- 
ture — have their normal activity seriously impaired by withdrawal 
of the sympathetic influence. 

The chief vaso-motor center is in the medulla, though accessory 
centers exist also in the cord ; all vaso-motor fibers pass out from 
these centers and leave the cerebro-spinal axis with the cranial 
or spinal nerves. 

The most usual mode of action of the vaso-motor nerves is 
reflex, as when the mucous membrane of the stomach becomes 
hyperemic upon the introduction of food \ or when the salivary 
secretion increases during mastication, or even sometimes at the 
sight or thought of food ; or when emotions are evidenced by 
paling or blushing. 

Raising blood-pressure by stimulating the vaso-constrictors 
and lowering it by stimulating the vaso-dilators are simply me- 
chanical results, and require no comment. For other remarks 
upon vaso-motor nerves see p. 177. 

Sleep. — Sleep is closely associated with vaso-motor action. 
Every part of the body has a function to perform, but it must 
have some rest from that performance or it will begin to act in- 
efficiently and finally cease altogether. For most organs these 
periods of rest occur at approximately uniform intervals, as in 
case of the stomach, heart or respiratory muscles ; but notably 
in case of the involuntary muscles these periods of repose have 
no regularity — i. e., a. person exercises them at no regular time 
except by accident of occupation or otherwise. But, in any 
case, there comes a time when repose must be had, for during 
activity the destructive processes far exceed the constructive, and 
in order for the balance to be preserved there must be a time 
when the opposite is true. 

Now we may say that it is the function of the brain to furnish 

consciousness — if we can allow that consciousness embraces all 

the various manifestations of nerve force peculiar to the brain. 

For the brain to suspend this function at frequent intervals like 

*4 



370 THE NERVOUS SYSTEM. 

the heart (e. g.) would be manifestly impossible if one is to do 
any consecutive work depending upon this organ. The brain 
works longer, and must, therefore, rest longer at a time than 
most of the other organs of the body. True, so far as the volun- 
tary muscles are concerned they rest best probably when the 
brain is resting, but the latter condition is not a necessary one 
for the maintenance of their physiological integrity. This repose 
of the brain — this temporary abolition of the cerebral functions 
— is sleep. While, of course, the activity of that organ during 
wakefulness may be increased or diminished by volition, and it 
may, therefore rest from a comparative standpoint — as when one 
ceases to think actively upon a subject and becomes mentally list- 
less — still the brain can never, under such circumstances, rest 
properly, and sleep finally becomes imperative. 

Vascular Phenomena of Sleep. — Coma is analogous to sleep 
in that consciousness is lost ; but in this case the brain is con- 
gested and the condition is unnatural. It was long supposed that 
this was the vascular condition during natural sleep, but appli- 
cation of the physiological principles prevailing in other parts 
of the body would rather presuppose a condition of cerebral 
anemia ; for the brain receives blood for two purposes — first, to 
supply nutrition to the nervous substance, and, second, to bring 
supplies which, by the action of the brain cells, may be con- 
verted into nerve force — and during sleep only the first of these 
purposes is to be served. This is true in case of glands, muscles, 
etc., during their intervals of repose. As a matter of fact, the 
cerebral vessels are coiitracted and there is much less blood in 
the brain during sleep than during consciousness. 

Dreams. — In explanation of the phenomena of dreams and 
somnambulism, it is said that what we call sleep may occur in 
one part of the brain and not in another, or in different degrees 
in different parts of the nervous centers. "In the former case 
[dreams] the cerebrum is still partially active ; but the mind 
products of its action are no longer corrected by the reception, 



THE SYMPATHETIC SYSTEM. 37 1 

on the part of the sleeping sensorium, of impressions of objects 
belonging to the outer world ; neither can the cerebrum, in this 
half-awake condition, act on the centers of reflex action of the 
voluntary muscles, so as to cause the latter to contract — a fact 
within the painful experience of all who have suffered from 
nightmare. In somnambulism the cerebrum is capable of exciting 
that train of reflex nervous action which is necessary for pro- 
gression, while the nerve center of muscular sense (in the cere- 
bellum?) is presumably fully awake ; but the sensorium is still 
asleep, and impressions made on it are not sufficiently felt to 
rouse the cerebrum to a comparison of the difference between 
mere ideas or memories and sensations derived from external 
objects" (Kirkes). 

Relation Between the Cerebro-spinal and Sympathetic Sys- 
tems. — A brief resume may help to clarify the association be- 
tween the two systems. 

1. Anatomically. — The two are developed from the same em- 
bryological tissue \ the vasomotor sympathetic fibers obey centers 
in the medulla and cord, and must, therefore, be connected with 
those centers either directly or indirectly; characteristic small 
medullated fibers pass at intervals from the cord through the 
roots into the sympathetic ganglia ; they send fibers each to the 
trunks of the other to be distributed directly, or to form plexuses 
and then be distributed together ; their fibers are found together 
in all organs which receive cerebro-spinal nerves (unless they 
be non-vascular); in some of these organs just named the sym- 
pathetic fibers are there only as vasomotor nerves, while in 
others, as glandular structures like the liver and salivary glands, 
sympathetic fibers are distributed to the gland cells themselves, 
and both have a definite but associated influence on secretion. 

2. Physiologically. — The physiological relation is best indi- 
cated by examples. A great many, if not all, the sympathetic 
ganglia seem to receive their power to generate nerve force from 
the cerebro-spinal system ; there can be no proper nutrition of the 



372 THE NERVOUS SYSTEM. 

parts animated by cerebro-spinal fibers without the associated ac- 
tion of vasomotor sympathetic fibers — not even of the nerve cells 
and fibers themselves ; in reflex action the afferent impression 
may be conveyed by a cerebro-spinal fiber and reflected through 
a sympathetic, or vice versa ; when one hand is thrust into hot 
or cold water the temperature of the opposite hand may be 
raised or lowered, impressions having been carried to the center 
by cerebro-spinal and reflected by sympathetic fibers, not only 
to the immersed hand, but to the other as well ; food is taken 
into the mouth, impressions are carried by nerves of common 
sensation to the brain and are reflected through the sympathetic 
system, an increased amount of blood is thereby sent to the 
salivary glands and an increased secretion supervenes \ one 
smells savory articles and the mouth waters, etc. 

Examples could be multiplied ad infinitum to establish the 
cooperation existing between the two systems. What has been 
incidentally and indirectly said on this point in considering 
secretion, digestion, circulation, respiration, etc., serves to em- 
phasize their connection. 



CHAPTER X. 
THE SENSES. 



It is evident from preceding remarks that it is through the 
intervention of the nervous system that we have a ( ( sense ' ' of 
existence, of the existence and condition of different parts of 
our bodies and of our relations to the external world. The 
knowledge we thus obtain is based upon sensations of various 
kinds, all of which are carried to the centers by afferent fibers. 
Such sensations may be what are termed (A) Common, or (i?) 
Special, including (i) Touch, (2) Smell, (3) Sight, (4) Smell, 
(5) Hearing. It is to be remembered that the seat of sensation 
is in the brain, and not in any organ which primarily receives or 
conveys the impression. We do not in reality see with the eye 
or hear with the ear ; these are only complex organs so arranged 
that rays of light or sound waves produce upon them such im- 
pressions as, when transmitted to the sensorium, will give rise to 
the sensations of sight or hearing. 

(A) COMMON SENSATIONS. 

As regards the uses of the fibers conveying impressions which 
result in these sensations, they (unless it be those concerned with 
tactile impressions) are distinct from those of special sense. That 
is to say, the fibers of the olfactory, optic, gustatory and auditory 
nerves do not convey general impressions ; but it is almost cer- 
tain that fibers conveying tactile impressions convey also pain- 
ful impressions — and the sensation of pain is taken as typical of 
common sensations. It is known that very painful impressions 
sometimes overcome tactile sensibility, and that very frequently 

373 



374 THE SENSES. 

tactile sensibility remains in parts which receive no painful im- 
pressions, as, e. g., under anesthesia by cocain ; but it may be 
that the power in the same fiber to convey, in the first case 
tactile, and in the second painful impressions is destroyed with- 
out destroying its power to convey the other. 

The varieties of common sensation are too numerous to even 
mention. Thirst, hunger, fatigue, discomfort, satiety, etc., are 
everyday examples, as are also the desire to urinate or defecate. 
Numerous subdivisions of the sensation of pain might be men- 
tioned, such as itching, burning, aching, etc. The so-called 
muscular sense — by which we become aware of the condition, 
relation, coordination and degree of activity or repose of the 
muscles — will be considered as belonging here. 

(B) SPECIAL SENSATIONS, 
i. The Sense of Touch. 

The sense of touch is closely related to common sensation. 
Its distribution over the body is as uniform as that of common 
sensation, but it is most highly developed in those parts where 
general sensibility is most marked (as in the skin), and attains 
its highest degree of perfection only in those situations in which 
tactile corpuscles exist, for example, on the palmar surfaces of 
the tips of the fingers. The teeth, hair, nails, etc., are rather 
surprisingly endowed with tactile sensibility. Leaving pain and 
the muscular sense as parts of general sensibility, the sense of 
touch may be considered under two heads — (a) Tactile Sensi- 
bility proper and (£) Temperature. 

(a) Tactile sensibility proper is most marked where the 
epidermis over the papillae is thin. When the epidermis is re- 
moved and the cutis is touched there is pain instead. Tactile 
sensibility is much decreased where the epidermis is thickened, 
as over the heel. The terminal tactile organs have been de- 
scribed in connection with afferent nerves. They are chiefly 
the end bulbs of Krause and the tactile corpuscles of Meiss- 



THE SENSE OF SMELL. 375 

ner. (See Figs. 68 and 69.) Besides, tactile impressions are re- 
ceived by the free extremities of afferent nerves situated over the 
body at large. Numbness from cold is due to interference with 
cutaneous circulation — upon which the sense of touch is directly 
dependent. It is almost impossible to distinguish mere touch 
from pressure. 

Acuteness. — How the sense of touch is capable of develop- 
ment by practice is well illustrated in the case of many blind 
persons. They learn to read with comparative facility by pass- 
ing the hand over raised letters ; or they frequently make the 
sense of touch take the place of the lost sense in other almost 
incredible ways. The acuteness of this sense in different por- 
tions of the body has been made the subject of observation by 
touching two different parts in the same region with finely 
pointed instruments and noting how near the points can be 
brought together and still be recognized as two. This distance 
is found to vary from ^ ¥ inch on the tip of the tongue to 2 y 2 
inches in the dorsal region. 

(£) It is not improbable that there are special nerve endings 
concerned in the reception of temperature impressions, though 
this has not been definitely proven. Decisions as to tempera- 
ture are only relative ; the surface temperature of the part upon 
which the impression is made is the standard, and one can only 
tell absolutely whether the object is hotter or colder than the 
skin, and, within certain limits, approximate how much hotter or 
colder. The delicacy of the temperature sense agrees with 
that of touch as regards the thickness or absence of the epi- 
dermis. 

2. The Sense of Smell. 

Regarding the mechanism of olfaction it is found that one of 
the first conditions necessary is the presence of particular cells. 
Between the epithelial cells of the mucous membrane to which 
the olfactory fibers are distributed are delicate spindle-shaped 
cells known as olfactory cells, and to them pass the terminal 



376 THE SENSES. 

filaments from the olfactory bulbs. These cells are stimulated 
by contact with odorous substances, and from them go, by way 
of the nerve fibers, impressions which are recognized as odors 
of different kinds. The olfactory fibers are the only ones which 
will convey such impressions. True, the same substance may, 
at the same time, excite other sensations, as of pain or taste, 
but the impressions giving rise to these latter sensations are con- 
veyed by different fibers altogether. The substances which ex- 
cite olfaction must come in actual contact with the nerve ter- 
minals and to do this must be dissolved in the mucus of the 
nasal mucous membrane; hence dryness of the nasal cavities 
(as in the first stage of nasal catarrh) interferes with olfaction. 
It is also said that odorous substances introduced in solution 
into the nasal cavities will not excite the sense of smell, but 
that they must be introduced by a current of air. 

Whether an odor is pleasant or unpleasant is largely a relative 
matter ; odors most disgusting to some animals are not offensive 
to others. This same difference may also hold good among 
different men. Impairment of the sense of taste, for some reason, 
follows a loss of the sense of smell. 

3. The Sense of Sight. 

It is not intended to go into a detailed consideration of the 
sense of sight, but some remarks on the normal eye and its 
action are in order. 

Protection of the Ball. — The orbital cavity has a pyramidal 
shape with its base forward. It contains the eye-ball, its mus- 
cles, some adipose tissue and most of the lachrymal apparatus. 
Above the orbit, the eye-brows prevent a flow of perspiration from 
the forehead on to the lid, and also shade the eye to some extent. 
The lids, when closed, entirely obscure the balls and protect them 
in front. On their free borders are rows of hairs (eye-lashes) 
curling away from the globe and shading and protecting it from 
dust. The lids are closed by the orbicular es palpebrarum and 



LACHRYMAL APPARATUS. 377 

opened by the levator es palpebrarum superiores. In the ordinary 
closing of the lids only the upper one is moved, but the lower 
one is raised in forcible contraction of the orbicularis. Inter- 
vention of the will is not necessary to the action of these muscles, 
though they are striated. Except during fatigue, the eyes are 
kept open involuntarily, but when the cornea is touched no 
effort of the will can prevent contraction of the orbicularis 
palpebrarum. During sleep the globes are rotated upward. 

The Lachrymal Apparatus. — This conists of the lachrymal 
glands, canal, duct and sac, and the nasal duct. The secre- 
tion of the lachrymal gland keeps the cornea and conjunc- 
tiva constantly bathed in a thin fluid. It is situated in the 
orbital cavity at its upper and outer portion. Its secretion is 
discharged upon the conjunctiva by several little ducts. The 
excess of secretion is carried into the nose through the nasal 
duct. Near the inner canthus is a small opening in each lid ; 
these openings are the orifices of the lachrymal canals, which 
canals join at the inner angle of the eye to form the lachrymal 
sac ; the sac is continued below as the nasal duct, opening 
into the inferior meatus of the nose. The secretion of tears 
is much diminished during sleep. The influence of the nervous 
system on lachrymal secretion is well known. Emotional dis- 
turbances operate through the sympathetic to increase the flow. 
Irritation of the mucous membrane of the nose or eye is fol- 
lowed by a like result. 

Movements of the Ball. — The capsule of Tenon, a fibrous 
membrane outside the sclerotic, holds the ball loosely in place. 
A small amount of adipose tissue behind the globe is never 
absent. Movements of the ball are effected through the ac- 
tion of the internal and external recti, the superior and inferior 
recti, and the superior and inferior oblique; of these, all but 
the two last named arise from the apex of the orbital cavity. 
The recti are inserted into the sclerotic just back of the cornea. 
The superior oblique runs along the inner aspect of the orbital 



378 



THE SENSES. 



cavity to a point near the supero-internal angle ; here it be- 
comes tendinous, passes through a fibro-cartilaginous ring, and 
then turns backward and outward to be inserted into the sclerotic 
between the superior and external recti just behind the center 
of the globe. The inferior oblique arises just within the orbital 

Fig. 85. 




Lateral View of the Muscles of the Eye-ball. 

5, trochlea or pulley of the superior oblique muscle, 12 ; 6, optic nerve ; 8, superior, 9, in- 
ferior, and 12, external rectus; 13, inferior oblique, (Landot's.) 



cavity near the anterior inferior angle, and passes around the 
anterior part of the globe to be inserted in the sclerotic just 
below the superior oblique. 

The effect these muscles have upon the movements of the ball 
is indicated by their origin and attachment. The external and 
internal recti rotate it outward and inward, the superior and in- 
ferior recti upward and downward. The superior and inferior 
oblique antagonize each other. The former rotates the globe so 



ANATOMY OF THE EYE-BALL. 379 

that the pupil is directed outward and downward ; the latter so 
that it looks outward and upward. The associated action 
of all these muscles can produce almost any variety of move- 
ments, and no effort of the will is necessary to properly associate 
them when it is desired to direct the line of vision toward a 
certain object. For instance, when it is desired to look at an 
object on the right it takes no distinct voluntary effort to con- 
tract the external rectus of the right eye and the internal rectus 
of the left. It will be seen later that vision for the two eyes is 
normal only when impressions are made upon exactly corre- 
sponding parts of the two retinae, so that they may act as a single 
organ ; and for this to be done not always the same movements 
are called for in both balls. 

Anatomy of the Ball. — The eye-ball is a globular body con- 
sisting of several coats enclosing refracting media. Of these 
coats the external is the sclerotic, dense and fibrous, covering 
the posterior five-sixths of the organ and continuous with the 
cornea, which covers the anterior one-sixth. It is not well sup- 
plied with blood-vessels. The cornea is transparent, and upon 
its external surface are several layers of delicate nucleated epithe- 
lium ; underneath this layer of cells is a thin membrane, the an- 
terior elastic lamella, which is a continuation of the conjunc- 
tiva. The substance proper of the cornea is composed of pale 
interlacing fibers among which are connective tissue corpuscles 
and quite a quantity of fluid. These fibers are continuous from 
the sclerotic, but they lose their opacity at the corneo-sclerotic 
margin. On the posterior surface of the cornea is the trans- 
parent elastic membrane of Descemet, a part of which, at the 
circumference of the iris, passes into the ciliary muscle. The 
cornea is very sensitive, but contains no blood-vessels. 

Next inside the sclerotic is the choroid coat of the eye. It 
does not lie under the cornea, but is confined to the sclerotic 
area of the ball. Behind the optic nerve penetrates it, and in 
front it is connected with the iris. The choroid is very vascular. 



3 8o 



THE SENSES. 



Its color is dark brown on account of the abundance of pigment 
in the cells on the inner surface of the membrane. Anteriorly 
the choroid is folded in upon itself to form the ciliary processes, 
which project inward around the margin of the crystalline lens. 
The ciliary muscle is important in accommodation. It is in 
the shape of a muscular ring surrounding the margin of the 
choroid just outside the ciliary processes. In front it is attached 

Fig. 86. 




Diagram of a Vertical Section of the Eye. (From Yeo after Holden.) 
i, anterior chamber filled with aqueous humor ; 2, posterior chamber ; 3, canal of Petit: 
a, hyaloid membrane ; b, retina (dotted line) ; c, choroid coat (black line) ; d, sclerotic 
coat ; e, cornea ; f, iris ; g, ciliary processes ; h, canal of Schlemm or Fontana ; i, ciliary 
muscle. 

to the line of junction of the cornea and sclerotic and to the 
ligament on the anterior surface of the iris ; behind it is lost 
in the substance of the choroid. Its contraction, therefore, com- 
presses the vitreous humor and relaxes the suspensory ligament 
of the lens. The iris is a circular veil hanging in front of the 
lens. It presents a perforation a little to the nasal side of its 
center, the pupil. It is attached in the corneo -sclerotic line. 
It contains circular and radiating fibers. The iris divides the 



THE RETINA. 38 1 

space between the cornea and lens into two chambers, anterior 
and posterior — the latter of which is very small. The " color 
of the eyes ' ' depends on the color of the anterior surface of the 
iris ; its posterior surface has a constant dark purple hue. The 
size of the pupil is subject to variations to be noted later. 

Inside the choroid is the retina, which is that part of the eye 
capable of receiving impressions of sight. Anteriorly it reaches 
nearly to the ciliary processes. Externally it is in contact with 
the choroid, and internally with the hyaloid membrane of the 
vitreous humor. It is penetrated by the optic nerve a little 
within and below the center of the posterior hemisphere. Just 
external to the point of entrance of the nerve is the macula 
lutea, a small yellow area in the center of which is the fovea 
centralis ; this last is exactly in the axis of distinct vision. Nine 
layers of cells are usually described as composing the retina. 
From without inward they are ( i ) the pigment layer, ( 2 ) rods 
and cones, (3-6) the four granular layers, (7) nerve cells, 
(8) expansion of fibers of the optic nerve, (9) the limitary 
membrane. Of these, the most important is the layer of rods 
and cones. The rods, or cylinders, extend through the thick- 
ness of the membrane and have between them, at intervals, flask- 
shaped bodies, the cones. At the macula lutea only the cones 
exist. Elsewhere the rods are more abundant than the cones. 
The length of the cones is about half that of the rods, and they 
occupy the inner aspect of the membrane. The layer of nerve 
cells presents cells communicating on the one hand with the rods 
and cones and on the other with fibers of the optic nerve. The 
rods and cones are the only parts of the retina possessing special 
sensibility, impressions being conveyed from them to the brain 
by the optic nerve. The fibers of the second nerve, composing 
one layer, are pale and transparent. The blood supply of the 
retina is from the arteria centralis retinae, which enters the optic 
nerve just before it expands, and, running in its substance, is 
distributed as far as the ciliary processes anteriorly. 



382 THE SENSES. 

The Crystalline Lens is a biconvex transparent body situ- 
ated just behind the iris. Its function is to refract the rays of 
light, and its action in this respect is similar to such lenses in 
optical instruments. It is held in place by the suspensory liga- 
ment. Its anterior convexity is more marked than its posterior. 
It is enveloped by a thin transparent capsule. 

The Suspensory Ligament is a continuation of the anterior 
layer of the hyaloid membrane of the vitreous humor. When 
this layer reaches the edge of the lens (coming forward) it 
divides into two parts, one passing in front of and the other 
behind that body ; the divisions are continuous respectively with 
the anterior and posterior portions of the capsule of the lens. 
The ligament supports the lens. 

The Aqueous Humor is behind the cornea and in front of 
the lens and suspensory ligament. The iris has been said to 
separate this cavity into anterior and posterior chambers com- 
municating through the pupillary opening. The aqueous x hu- 
mor is colorless and perfectly transparent. It serves to refract 
the rays of light, having for that purpose the same index as the 
cornea. 

The Vitreous Humor occupies about the posterior two-thirds 
of the globe, and is back of the lens and suspensory ligament 
surrounded by the delicate hyaloid membrane. It is of a gelat- 
inous consistence, and is divided into numerous compartments 
by very delicate membranes radiating from the point of entrance 
of the optic nerve. It is a transparent refracting medium. 

Ocular Refraction. — In order for the image of an object to be 
distinct the rays passing from it must fall on a single portion of 
the retina, viz., the fovea centralis. The sensibility of the 
retina to light decreases in passing away from the fovea. All 
rays would not meet on the retina unless they were refracted ; 
and for this purpose there are the cornea, the aqueous humor, 
the lens and the vitreous humor. The surfaces of the cornea 
and lens are the most important of these. Since the two sur- 



ACCOMMODATION. 383 

faces of the cornea are parallel, the external surface alone is con- 
cerned in refraction. The center of distinct vision (fovea) is 
in the axis of the lens precisely in the plane upon which the 
rays of light are brought to a focus by the refracting media. Re- 
fraction by the cornea alone would focus the rays behind the 
retina ; hence the necessity of convex lenses before the eye after 
operations for cataract. Rays leaving the cornea are refracted 
by the anterior surface of the lens, by its substance to a certain 
extent, and again by its posterior surface, the normal mechan- 
ism being such that all rays are focused on the fovea. The rays 
cross each other after refraction, and the image is inverted, but 
the brain takes no notice of this fact, and objects are seen in 
their natural positions. 

Accommodation. — Accommodation means a change in the 
convexity of the lens, whereby images are focused on the retina, 
whether the object be far away from or near the eye. Rays of 
light from distant objects strike the eye practically parallel, and 
we may assume that there is a certain "passive " condition of 
the refracting media which will bring such rays to a focus at the 
proper point. But when the object observed is near the eye a 
change in the arrangement of the media, or of the convexity of 
their surfaces, is necessary to prevent the focusing of the rays 
behind the retina. The desired end is accomplished by increas- 
ing the convexity of the lens. When the ciliary muscle is 
"passive" the capsule compresses the lens, decreasing its con- 
vexity to a minimum ; from the attachments of this muscle, 
already noted, its contraction is attended by a relaxation of the 
suspensory ligament, which in turn relieves in some degree the 
compression of the capsule upon the lens and allows its antero- 
posterior diameter to increase ; the result is increased convexity 
of the lens. 

When distant objects are looked at the lens become flatter as 
a result of contraction of the suspensory ligament, which contrac- 
tion is a consequence of the relaxation of the miliary muscle. 



384 THE SENSES. 

Accommodation for distant objects seems a passive process en- 
tirely. 

The ciliary muscle is the " muscle of accommodation." 

The contraction of the pupil for near objects is not, properly 
speaking, a part of accommodation. 

Then, granting special sensibility to the retina and optic 
nerve, the formation and appreciation of an image is simple. 
Rays of light having passed through the cornea and aqueous 
humor are admitted by the pupil to pass through the lens and 
vitreous humor. By all these objects they are refracted so that 
they cross each other and fall upon the retina, producing an in- 
verted image there. The size of the pupil, other things being 
equal, is regulated by the intensity of the light, the opening 
being contracted to admit less when the light is strong. 

Myopia, Hyperopia and Presbyopia. —Sometimes the antero- 
posterior diameter of the eye -ball is too long and the rays of 
light are brought to a focus in front of the retina. Such a con- 
dition is known as myopia ; the person will be near-sighted. 
He brings objects near his eyes so that the rays may have a 
greater divergence and thus be focused farther back. Or the 
rays may be scattered by placing concave lenses before the eyes. 
Sometimes, too, the antero-posterior diameter may be too short 
and the rays come to a focus behind the retina. Such a condi- 
tion is known as hyperopia ; the person will be far-sighted. 
He holds objects far away from his eyes that the rays from them 
may strike the ball with less divergence and thus be focused 
farther forward. Or the same end may be accomplished by 
placing convex lenses before the eyes. In old age the lens be- 
comes flattened and accommodates itself less easily. This tends 
to focus light behind the retina and objects have to be held far 
away from the eye. This is known as presbyopia. Its remedy 
is the same as that for hyperopia. 

Reaction to Light. — Regarding the reaction of the pupil to 
light, it is evident that this is mainly a reflex nervous phenom- 



THE SENSE OF TASTE. 385 

enon, though direct light will cause the muscular tissue of the 
iris to contract. The direct influence of the third nerve on the 
action of the iris has been referred to under a consideration of 
that nerve. Reflexly, the pupil is contracted by light by the 
conveyance of an impression to the brain through the optic 
fibers ; a message is sent to the proper center, and a stimulus 
is reflected through the third nerve to the sphincter of the iris caus- 
ing it to contract. When the optic nerve is cut the circuit is 
broken, and movements of the iris do not occur from the admis- 
sion of light. Practically, then, when much or little light reaches 
the retina the pupil contracts or dilates, as the case may be, in 
an effort to keep the amount constant. 

Binocular Vision.— It is evident that when a person looks at 
an object two images are formed— one on each retina— but they 
are combined in his consciousness and he sees but one object. 
If one of the balls be thrown out of the proper axis, by pressure, 
e. g., objects appear double. The same is true in strabismus, at 
least until the person has grown accustomed to the defect. In 
normal vision the rays from an object are formed on the fovea 
centralis of each eye— that is, upon corresponding points which 
are, for each, the centers of distinct vision. 

4. The Sense of Taste. 

In order that gustatory sensation may be excited it is neces- 
sary (1) that there be specially endowed nerves and nerve 
centers ; (2) that the nerve terminals be excited by sapid (tast- 
able) materials; (3) that these substances be in solution. It 
has already been seen that the special nerves of taste are (a) 
the chorda tympani distributed to the anterior two-thirds of the 
tongue, and (b) the glossopharyngeal to the posterior third of that 
organ. It is probable that only the dorsum of the tongue, the 
lateral parts of the soft palate, the uvula and the upper pharynx 
are concerned in gustation. On the tongue are found special 
papillae, (1) the circum vallate, large and few in number, near 
25 



386 THE SENSES. 

the base of the organ, and (2) the fungiform, about 200 in num- 
ber, over the remaining area. The circumvallate and some of the 
fungiform papillae contain taste beakers, true gustatory organs. 
They are ovoid collections of cells beneath the epithelial cover- 
ing of the mucous membrane. Sapid substances enter these 
beakers in solution and come in contact with the taste cells, 
which are connected with the filaments of the gustatory nerves. 
Thus are produced specific impressions which are conveyed to 
the gustatory center, and the sense of taste is excited. The 
limited distribution of the taste beakers makes it impossible 
that they should be the only organs capable of receiving special 
gustatory impressions. The taste center has been indefinitely 
located in the uncinate gyrus near the olfactory center. 

Since it is necessary to the tasting of substances that they 
come in actual contact with the taste organs, and since to do so 
they must be in solution, it follows that dryness of the mouth 
interferes with, or abolishes, this sense. 

The most marked tastes are the sweet, bitter, saline, and 
alkaline. The more delicate flavors involve also the special sense 
of smell, and it has been seen that dissociation of the two kinds 
of impressions is often impossible. Taste is also subject to va- 
riations by reason of education, age, association, caprice, etc. 
Bitters are most easily appreciated at the back, salts and sweets 
at the tip, and acids at the sides of the tongue. 

5. The Sense of Hearing. 

The ear consists of a complicated apparatus for the purpose 
of the reception of special impressions which are appreciated by 
the brain as sounds. Anatomically it consists of the external, 
the middle and the internal ear ; the last contains the essentials 
of the auditory apparatus, the external and middle divisions serv- 
ing only to concentrate the sound waves upon the parts of the 
internal. 

The External Ear. — This consists of the pinna and the ex- 



THE SENSE OF HEARING. 



387 



ternal auditory canal. The pinna is the external visible por- 
tion, and consists of the large cavity, the concha, into which the 
external auditory canal opens externally ; of two prominent 
ridges partly surrounding the concha, the helix outside and the 
antehelix internal to this ; and of a fibrocartilaginous process 
projecting backward in front of the concha, the tragus. The 

Fig. 87. 




Scheme of the Organ of Hearing. 
AG, external auditory meatus ; T, tympanic membrane; K, malleus with its head (h), 
short process (kf) and handle (m) ; a, incus, its short process (x) and its long process united 
to the stapes (s) by means of the Sylvian ossicle (Z) ; P, middle ear ; o, fenestra ovalis ; r, 
fenestra rotunda ; x, beginning of the lamina spiralis of the cochlea ; pt, scala tympani, and 
vt, scala vestibuli; V, vestibule ; S, saccule; U, utricle; H, semicircular canals; TE, 
Eustachian tube. The long arrow indicates the line of traction of the tensor tympani ; the 
short curved one, that of the stapedius. (Landozs.) 

external auditory canal runs inward and slightly forward from 
the concha to terminate at the membrana tympani, or drum. Its 
inner part is in the petrous portion of the temporal bone ; its 
external part is fibro -cartilaginous in structure. The whole is 
lined by integument. 



388 THE SENSES. 

The Middle Ear (Tympanum). — This is a cavity at the 
bottom of the external auditory canal in the petrous portion of 
the temporal bone, containing ossicles for the conduction of 
sound waves to the internal ear. The cavity communicates, 
through the Eustachian tube, with the pharynx, and this is its 
only direct connection with the external air, though it does 
communicate with the mastoid air cells. It is lined by mucous 
membrane. The membrana tympani, separating it from the 
external auditory canal, is fibrous in structure. It is lined ex- 
ternally by skin and internally by mucous membrane. 

The three ossicles of the middle ear are the malleus, incus 
and stapes. The malleus, shaped like a hammer, is attached 
in a vertical direction to the upper radius of the membrana 
tympani, and articulates by its head with the incus. The incus 
has the shape of an anvil ; its base articulates with the malleus, 
while its small extremity curves downward to articulate with the 
neck of the stapes. The base of the stapes is applied to the 
membrane covering the fenestra ovalis. The tensor and laxator 
tympani are attached to the neck of the malleus ; the stapedius 
to the neck of the stapes. These bones constitute a chain, 
which conveys the vibrations of the membrana tympani to the 
fenestra ovalis. 

The Internal Ear (Labyrinth). — This consists of a series 
of cavities in the petrous portion of the temporal bone lined 
by a peculiar membrane. When the bony substance surround- 
ing these cavities is carefully removed it is found that that por- 
tion immediately outside them is harder than the adjacent struc- 
ture. This constitutes the bony labyrinth, while the membrane 
inside the bony walls is the membranous labyrinth. 

The bony labyrinth consists of the vestibule, cochlea and 
semicircular canals. The vestibule occupies the mid-portion 
of the labyrinth, and is that part with which the middle ear com- 
municates by the fenestra ovalis ; it communicates also with the 
cochlea and semicircular canals, and on its internal aspect are 



THE INTERNAL EAR. 



3*9 



openings for the entrance of some of the branches of the audi- 
tory nerve. The cochlea, shaped like a snail shell, runs off 



Fig. 




I, Transverse section of a turn of the cochlea ; II, A, ampulla of a semicircular canal with 
the crista acustica; a, auditory cells, p, provided with a fine hair; T, otoliths ■ III 
scheme of the human labyrinth; IV, scheme of a bird's labyrinth; V, scheme of a fish's 
labyrinth. ( Landois. ) 

from the front of the vestibule, winds about two and a half 
times around a cone-shaped central axis— the modiolus— and 



39° THE SENSES. 

ends in a blind apex. The canal of the cochlea is partially sepa- 
rated into two compartments by a bony plate, the lamina spi- 
ralis. The basilar membrane completes the septum and divides 
the lumen of the cochlea into two canals, the scala tympani 
and the scala vestibuli, corresponding in name to the tympanic 
and vestibular openings of the cochlea. The semicircular 
canals, three in number — superior, external and posterior, — de- 
scribe arches from the posterior aspect of the vestibule, com- 
municating by both their extremities with that cavity. 

The membranous labyrinth consists of a special membrane 
lying inside the bony labyrinth and corresponding in general 
outline to the walls of the cavity. It is, however, separated 
from the walls by perilymph, and encloses a similar fluid, the 
endolymph. It covers the sides of the lamina spiralis in the 
cochlea and completes the septum, besides following the wall 
proper ; and on one side it sends a distinct process from the tip of 
the lamina spiralis to the wall of the canal, so that there are in 
reality three divisions of the lumen of the cochlea. This process 
is the membrane of Reissner, and the third canal is the scala 
media — the true membranous cochlea. (See Fig. 88.) 

Termination of Auditory Nerve. — The membranous labyrinth, 
containing and being suspended in fluid, receives the terminal 
filaments of the eighth nerve as well as all the sonorous vibra- 
tions intended for that nerve. When the auditory nerve has 
reached the base of the internal auditory meatus it enters the in- 
ternal ear by two divisions, one for the vestibule and semicir- 
cular canals and the other for the cochlea. The vestibular por- 
tion again subdivides, sending one branch to the utricle and 
superior and horizontal semicircular canals, and another to the 
saccule and posterior semicircular canal. The fibers of the 
eighth nerve spread out over the inner surface of the membrane 
to end in a way somewhat obscure. The membrane is lined in- 
ternally by epithelium whose character differs in different areas. 
In the region of distribution of the vestibular portion of the 



FUNCTIONS OF THE COCHLEA. 39 1 

nerve the cells are of two kinds, hair cells and rod cells. From 
the inner ends of the hair cells ciliated processes project into 
the endolymph ; to their outer ends pass the axis cylinders of 
the nerve fibers, though the exact mode of connection is not 
clear. The rod cells are much more numerous than the hair 
cells, but their precise connection with audition is not apparent. 

Upon the basilar membrane are the rods of Corti. They con- 
sist of two sets of pillars of varying length, slanting toward each 
other, thus leaving at their base a space which becomes a canal 
by a longitudinal succession of these pillars. There are sup- 
posed to be about 4,500 elements in the outer and 6,500 in the 
inner set of these rods. Intimately associated with the pillars 
are large numbers of hair cells with which the auditory nerve 
filaments may communicate \ it is certain that these filaments are 
closely connected in some way with the pillars. 

Functions of the Semicircular Canals. — The use of these is 
obscure. Their destruction is not followed by interference with 
hearing, although auditory filaments are distributed to some 
parts of them. Curiously enough, however, this lesion is one of 
the three chief ones interfering so markedly with equilibration — 
the phenomena following it being not unlike those sequent upon 
lesions of the cerebellum and the posterior white columns of the 
cord. 

Functions of the Cochlea. — While the exact mechanism of 
the production of auditory impressions is unknown, there seems 
to be no doubt that such mechanism takes place almost entirely 
in the cochlea, and that fibers which convey to the auditory cen- 
ters impressions of sound are distributed to the organ of Corti 
therein. That is to say, loss of the sense of hearing supervenes 
upon destruction of this part of the internal ear. In physics it 
is known that for a sound, for example of a piano string, to be 
heard the membrana tympani must vibrate in unison with the 
sonorous vibrations of the cord \ that is, " consonating bodies " 
repeat sonorous vibrations, giving them their proper pitch and 



392 THE SENSES. 

quality. It has been supposed that the thousands of rods of 
Corti, of varying length and size, in the cochlea are made to 
vibrate separately or in correctly associated collections (like the 
strings of a harp), and thus reproduce communicated vibrations, 
and so give rise to impressions which, conveyed by the auditory 
nerve to the center, are there recognized as sounds of different 
degrees of intensity, pitch and quality. This theory maybe 
true, but its correctness is probably beyond the range of experi- 
mental proof. 

While the usual mode of conduction of sound waves to the 
cochlea is through the external ear, they may reach it in other 
ways, as through the bones of the head, or through the Eustachian 
tube. Nor is the integrity of the membrana tympani actually 
necessary to the production of sound ; although practically speak- 
ing a person in whom this organ is destroyed is deaf, he can hear 
if the ossicles can in some way be placed in vibration by sound 
waves, as by the intervention of an artificial membrane. In- 
deed it has already been seen that none of the parts of the 
external or middle ear are actually necessary to hearing. They 
are only accessory conveniences for the better transmission of 
impressions to the filaments of the auditory nerve. 

The (so-called) tensor and laxator tympani muscles make 
tense or lax the membana tympani, thus influencing the rapidity 
and amplitude of its vibrations, and therefore the pitch and in- 
tensity of the sound. The stapedius prevents too great move- 
ment of the stapes. The free communication of the air in the 
tympanum with that in the mastoid cells and pharynx insures 
an approximately constant internal pressure upon the membrane, 
and thus precludes accidents which would otherwise interfere 
with its proper vibration. 

The auditory center in man is in the first and second temporal 
convolutions of the temporo-sphenoidal lobe. 

Briefly then, the physiology of hearing is as follows : Sound 
waves collected by the pinna enter the external auditory canal 



THE VOICE. 393 

and impinge upon the membrana tympani. The drum is thus set 
to vibrating and communicates its movements to the ossicles, 
which in turn hand them over through the fenestra ovalis to the 
fluids of the internal ear, through which media they reach the 
auditory filaments, are conducted to the brain and given proper 
recognition. 

The Production of the Voice. 

The production of the voice is not connected with the special 
senses, but its consideration will be introduced here for the 
sake of convenience. 

The Larynx is the organ of voice. It is a cavity closed ex- 
cept for its openings above and below. It consists of four car- 
tilages — cricoid, thyroid and two arytenoid — joined together by 
ligaments and muscles. The vocal cords are attached poste- 
riorly to the bases of the movable arytenoid cartilages and ante- 
riorly to the angle between the alae of the thyroid. The muscles 
serve to move the cartilages and thus to separate or approximate 
and to render lax or tense the vocal cords. 

Production of Sound. — The human voice is produced by 
vibrations of the vocal cords, which vibrations are set up by cur- 
rents of expired air. 

Movements of the Vocal Cords. — These are those taking 
place (i) in respiration and (2) during vocalization. 

1. In Respiration. — When the cords are "passive" they 
are approximated anteriorly and separated posteriorly, so that 
the interval between them (rima glottidis) is triangular. This 
interval becomes a little wider during inspiration and a little 
narrower during expiration. 

2. In Vocalization. — The production of sound in the larynx 
involves an approximation of the cords and an increase in their 
tension. They are made more nearly parallel by the approach 
of the arytenoids to each other, and the rima glottidis assumes 
the shape of a mere chink. The tenser the cords, the higher the 



394 THE SENSES. 

note produced ; usually also the closer the cords are brought to- 
gether, the higher the note. The range of the voice depends 
principally on the degree of tension which the cord can be 
made to assume. 

Varieties of Vocal Sounds. — These are mainly (i) monoto- 
nous, (2) transitional, (3) musical. 

1. In monotonous sounds the notes have all nearly the same 
pitch, as in reading. 

2. In transitional sounds there is a gradual change in the 
tension and approximation of the cords, so that the notes become 
successively higher or lower, as in the howling of a dog. 

3. In musical sounds the vocal cords have a definite number 
of vibrations for each successive note — a number corresponding 
to the production of that note in the musical scale. 

The range of the average human voice is from one to three 
octaves. The highest and lowest notes of females are about one 
octave higher than the corresponding notes of males. The chief 
difference between male and female voices is, therefore, one of 
pitch ; but they also differ materially in tone. The difference 
in pitch is a result of the different length, and therefore the dif- 
ferent rate of vibration, of the cords in the two sexes. The 
female cords are about two -thirds the length of the male. 

Before puberty the male larynx resembles the female, but at 
that period the alae of the thyroid become more prominent in 
the male and the cords increase in length, thus accounting for 
the change of voice. 

In old age control of the musculature of the larynx is partly 
lost, the cords become altered and the cartilages ossify. These 
circumstances make the voice weak and unsteady. 

Speech. — Modifications and alterations of the sounds produced 
in the larynx during and after their production result, under the 
influence of the sensorium, in articulate speech. These modifi- 
cations are made chiefly by the tongue, teeth and lips. 

The speech sounds are divided into vowels and consonants. 



NERVE SUPPLY OF THE LARYNX. 395 

The distinction is that the vowel sounds are generated in the 
larynx, while the consonant sounds are produced by alterations 
in the current of air above the larynx, and cannot be pronounced 
except consonantly with a vowel. The current is modified 
mainly by the tongue and teeth in the formation of Unguals and 
dentals, by the cavity of the nose in case of nasals, and by 
changes in the shape and size of the oral cavity in the produc- 
tion of other sounds. 

Nervous Supply of the Larynx. — The superior laryngeal 
branch of the tenth is the sensory nerve, which guards the glottis 
to prevent the entrance of foreign bodies. Impressions made 
on the filaments of this nerve are reflected through the medulla 
and inferior laryngeal branch of the tenth to the muscles which 
close the glottis. The inferior laryngeal also innervates the 
muscles that vary the tension of the cords, and the superior 
laryngeal keeps the mind informed of the state of these muscles 
and of the necessity for forced expiration or coughing. 



CHAPTER XI. 
REPRODUCTION. 



Very many facts in our knowledge of reproduction depend 
on observations made upon lower animals, but there is sufficient 
analogy between the known facts connected with human repro- 
duction and development and those of the same stages in other 
groups of beings to enable us to present, as at least approxi- 
mately accurate, certain broad principles regarding the process 
as it pertains to the human race. 

In order that a human being may be brought into existence it 
is necessary that there be a union of the male element, the 
spermatozoon, and the female element, the ovum. Both these 
sexual cells are developed from epithelium — the spermatozoon 
from that of the seminiferous tubules of the male, and the ovum 
from the germinal layer of the ovary. 

In what follows reference will be had to reproductive proc- 
esses in the human being. 

Spermatozoa. — Human spermatozoa (Fig. 89) are elongated 
bodies, about one five -hundredth of an inch in length, and con- 
sist of three parts, head, mid -portion and tail. The last-named 
part is about four-fifths the length of the entire spermatozoon. 
The head is egg-shaped and much the thickest part of the ele- 
ment. A slender filament, the axial fiber, extends throughout 
its length from head to tail and projects slightly beyond the latter. 
Spermatozoa are possessed of wonderful vitality. They live for 
several weeks in the genital passages of the female. In the male 
genital passages they may live for months in a quiescent state. 

396 



SPERMATOZOA. 



397 



The nucleus is the fertilizing agent. Spermatozoa are also 
remarkable for their power of locomotion, which is effected by 
lashings and rotary movements of the tail. 

Ova. — The ovum (Fig. 90), or female sexual cell, is the largest 
cell to be found in the human body. Its diameter is about T | T of an 

Fig. 89. 




Spermatozoa. 
1, human (X 600), the head seen from the side ; 2, on edge; k, head; m, middle piece ; f. 
tail; e, terminal filament ; 3, from the mouse ; 4, bothriocephalus latus ; 5, deer ; 6, mole ; 7, 
green woodpecker; 8, black swan; 9, from a cross between a goldfinch (m.) and a canary 
(f.) ; 10, from cobitis. {Landois.) 



inch. Its structure is that of a typical cell. When the ovary is de- 
veloping a part of its covering epithelium dips down into the sub- 
stance of the organ and becomes walled off by union of the sur- 
face cells above it. A part of this ball of epithelium becomes 
the ovum, and a part the Graafian follicle for that ovum. 



39* 



REPRODUCTION. 



Fig. 90. 



The youngest ova are thus found nearest the surface of the ovary. 
The cell has an enveloping membrane, the vitelline membrane, a 
protoplasm, the vitellus, a nucleus, the ger??iinal vesicle, and a 
nucleolus, the germinal spot. Outside the ovum, but not strictly 
a part of it, is the zona pellucida, a transparent envelope, and 
outside the zona pellucida a collection of cells, the corona 
radiata. The perivitelline space is between the ovum proper 
and the zona pellucida. The zona presents radial striae, which 
may facilitate the entrance of the spermatozoon. 

Ova are capable of being impregnated as long as 7-9 days after 
their discharge from the ovary. Their formation begins early 

in fetal life. The ovum pos- 
sesses no power of independent 
motion. It is passive in fecun- 
dation ; it is sought by the male 
element. Its vitellus, or yolk 
(protoplasm), contains nutritive 
non-living material, deutoplasm, 
whose function is to furnish food- 
substance to the impregnated 
ovum until the fetal circulation 
is established. Deutoplasm in 
the human ovum is scarcely to be 
distinguished from the living 
protoplasm, though in the ova 
of birds, e. g., it is clearly 
marked off, and constitutes the 
main bulk of the mature egg, 
since the developing embryo receives no blood from the mother. 
Graafian Follicles. — The Graafian follicles are directly con- 
cerned in the development and maturation of ova. These are 
small vesicles in the cortical ovarian substance surrounded by a 
capsule of thickened ovarian stroma, the tunica vasculosa. In- 
side the tunica vasculosa, lining the ■ spherical cavity of the 




Ovum. (From Yeo after Robin.) 
a, zona pellucida and vitelline membrane; 
b, yolk ; c, germinal vesicle or nucleus ; d, 
germinal spot or nucleolus ; e, interval left 
by the retraction of the vitellus from the 
zona pellucida. 



GRAAFIAN FOLLICLES. 



399 



vesicle, are several layers of epithelial cells making up the 
me?nbrana granulosa. The cavity is filled with an albuminous 

Fig. 91. 




CAD 'AT.t^ 



Section of the Ovary of a Cat, Showing the Origin and Development of 
Graafian Follicles. (From Yeo after Cadiat.) 

a, germ epithelium ; b, Graafian follicle partly developed ; c , earliest form of Graafian 
follicle ; d, well-developed Graafian follicle ; e, ovum ; f, vitelline membrane ; g, veins ; h, i, 
small vessels cut across. 

liquid, the liquor fo Hi culi. At one point in its circumference the 
membrana granulosa is much thickened, and in this thickened 
portion is imbedded the ovum. The epithelial cells of the 



4-00 REPRODUCTION. 

membrana completely surround the ovum, constituting the discus 
proligerus. The cells of the discus next the ovum have their 
long axes at right angles to the circumference of the egg, and 
this layer is the corona radiata already mentioned. The zona 
pellucida is just underneath the corona. 

Usually a Graafian follicle contains only one ovum. The 
follicles and their contained ova begin to be formed early in fetal 
life. Probably none are newly formed after the child is two 
years old, but they are undeveloped before puberty. It is esti- 
mated that some 72,000 follicles and ova exist in the two ovaries 
of the average woman ; but of these not more than 400 reach 
full development, the others undergoing retrograde changes and 
disappearing. 

Up to puberty the follicles and ova are small, but at that time 
some of them begin to enlarge, and at more or less regular inter- 
vals one of these follicles bursts and allows the escape of its con- 
tained ovum into the fimbriated extremity of the Fallopian tube 
— a process known as ovulation. Previous to its rupture the 
Graafian follicle has been enlarging. It is always located in the 
cortical part of the ovary, but it may now not only form a dis- 
tinct protrusion above the surface of the organ, but may by its 
size encroach upon the medullary portion. It may at this time 
have a diameter of half an inch. Meantime the more superficial 
part of the tunica vasculosa has been undergoing fatty degener- 
ation, has lost its blood supply and become very thin. Here 
rupture occurs, and the mature ovum, ready for impregnation, 
escapes upon the surface of the ovary. 

Corpus Luteum. — When the ovum has been extruded hem- 
orrhage occurs, filling the empty follicle with blood. By con- 
traction of the extra-vesicular adjacent tissue the walls of the 
Graafian follicle become folded into the cavity. Soon prolifera- 
tion of the cells of the follicular wall takes place into the blood 
clot, vascular loops are formed, and the tunica vasculosa itself 
becomes greatly hypertrophied. The clot later disappears and 



CORPUS LUTEUM. 



401 



the mass then has a yellowish color and is known as the corpus 
hit cum. 

Whether or not the ovum that escaped from the follicle which 
was the antecedent of any given corpus luteum was impreg- 
nated, has an influence upon the growth of that corpus. If the 
ovum failed of fecundation the corpus luteum will reach its 
highest development in about fifteen days, and will then assume 
the character of cicatricial tissue and be absorbed in a few 
weeks. If the ovum was fecundated, the corpus luteum will 
increase in size for some three months, until it may be half the 
size of the ovary. At labor it has been reduced to a white 
cicatrix, which probably persists as a small nodule throughout 
life. The differences between the corpora lutea of menstrua- 
tion and pregnancy are shown by the following table from 
Dalton : 

Corpus Luteum of Menstruation. Corpus Luteum of Pregnancy. 

At the end of Three-quarters of an inch in diameter ; central clot 

three weeks. \ reddish ; convoluted wall pale. 

One month. Smaller ; convoluted wall I Larger ; convoluted wall 

bright yellow ; clot still | bright yellow ; clot still red- 
dish. 

Seven-eighths of an inch 
in diameter ; convoluted ; 
wall bright yellow; clot per- 
fectly decolorized. 

Seven-eighths of an inch 
in diameter ; clot pale and 
fibrinous ; convoluted wall 
dull yellow. 
Absent. Still as large as at the 

end of second month ; clot 
fibrinous ; convoluted wall 
paler. 
Absent. Half an inch in diameter ; 

central clot converted into a 
radiating cicatrix ; external 
wall tolerably thick and con- 
voluted, but without any 
bright yellow color. 



Two months. 



Four months. 



Six months. 



Nine months. 



reddish. 

Reduced to the condition 
of an insignificant cicatrix. 

Absent or unnoticeable. 



Maturation. — But previous to its discharge from the Graafian 
follicle, the ovum undergoes certain changes— a ripening process 
26 



402 



REPRODUCTION. 



— whereby it is made ready to receive and be impregnated by 
the spermatozoon. This maturation consists in the discharge 
from the cell proper of a part of its nucleus and a part of its 
protoplasm. The nucleus moves toward the periphery, and the 
perinuclear membrane is lost. As the nucleus approaches the 
surface of the egg it undergoes karyokinesis, and a part of it, 
together with a little surrounding protoplasm, is extruded and 

Fig. 92. 



Zona 
pc/Iucida 




Polar globules 



The Fertilized Ovum, or Blastosphere. (Kirkes.) 



finds itself in the perivitelline space. This is the first polar body. 
A second polar body is likewise later discharged by karyokinetic 
division. (See Fig. 92.) 

The object of this extrusion and the final fate of the polar 
bodies are matters of speculation. That portion of the nucleus 
which remains after the polar bodies have been thrown off finds 
its way back to the center of the ovum. It soon develops a cover- 
ing membrane, and is now the female pronucleus, ready for union 
with the male pronucleus. It is about the time of the completion 
of this process that the follicle ruptures and the discharge of the 
ovum — ovulation — occurs. 

Ovulation. — It is supposed that from puberty to the meno- 
pause one (or more?) ovum is discharged at tolerably regular 
intervals of about four weeks. It should, and usually does, enter 



MENSTRUATION. 403 

the outer end of the Fallopian tube, to be conveyed toward the 
uterus. Obviously only a few, and sometimes none, are ever 
impregnated. Should the ovum fail to reach the uterus and 
become fecundated, ectopic gestation will be the result. 

The patent fimbriated extremity of the tube may grasp the 
ovary at the time of rupture of the Graafian follicle, but this is 
not probable. One of the tubal fimbriae is attached to the outer 
extremity of the ovary and has on its surface a small linear de- 
pression lined by ciliated epithelium and leading to the tube. 
The ovum very likely in most cases drops into this depression, 
and the influence of the cilia is to carry it towards the tube. 

Menstruation. — Usually between the fourteenth and seven- 
teenth years of female life menstruation begins. It is a discharge 
of blood, epithelium and other parts of the mucous membrane of 
the uterine cavity, together with mucus from the glands of the 
uterus and vagina. About the beginning of menstrual life there 
are marked changes in bodily development, Graafian follicles 
enlarge and begin to approach the surface, ovulation is begun, 
and the female is capable of being impregnated. 

In most cases menstruation occurs at regular intervals of 
twenty-eight days. The function is suspended during pregnancy 
and usually during lactation. When it is first established it is 
frequently irregular in its occurrence for several months ; a like 
irregularity usually accompanies the cessation of the function 
between the fortieth and fiftieth years — when the menopause, or 
climacteric, is established. The normal female may be impreg- 
nated during menstrual life, but not before or after. 

The average length of time for which the menstrual flow con- 
tinues is four days. There are many exceptions in both direc- 
tions for different women, but the time for any one woman 
probably varies little under normal conditions. The discharge 
for each period averages some five ounces. It does not usually 
coagulate, on account of the presence of alkaline mucus. For 
five- or six days preceding the flow, the uterine mucous mem- 



404 REPRODUCTION. 

brane gradually thickens, the glands become longer and more 
tortuous, the connective tissue cells multiply and the blood 
vessels are greatly increased in size. This is apparently a prep- 
aration for the reception of the impregnated ovum. A short 
time before the flow begins there is hemorrhage into the subepi- 
thelial tissue, possibly by diapedesis, possibly by rupture. In a 
day or so the superjacent mucous membrane becomes disinte- 
grated and is discharged with the included parts of the glands. 
The underlying vessels, being thus- exposed, rupture and the san- 
guineous discharge carries away the debris. 

For three or four days subsequent to the cessation of the flow 
the uterine mucosa is being repaired. The deeper layers, in- 
cluding the deeper portions of the glands, were not cast off, and 
the whole is reconstructed from the intact parts. Following the 
reconstructive period there is a stage of quiescence lasting some 
two weeks, until six or seven days prior to the next menstrua- 
tion. 

At the beginning of each menstrual flow there is general con- 
gestion of the pelvic viscera and mammary glands, accompanied 
usually by headache and a sense of pelvic oppression. The 
congestion and discomfort begin to disappear when the flow is 
established. 

Ovulation probably in most cases takes place just before the 
menstrual flow begins, but neither occurrence is dependent upon 
the other. Ovulation has frequently been shown to take place 
in the inter-menstrual period, but the congestion of the repro- 
ductive organs incident to menstruation probably hastens the 
rupture of any Graafian follicle which at that time happens to 
be near the completion of its development. 

The relations between ovulation, menstruation and impregna- 
tion are not definitely determined. Pregnancy lasts for ten 
lunar months and dates from the time of impregnation (concep- 
tion), but that time cannot in any case be fixed upon with pre- 
cision. The vitality of the ovum is thought not to last longer 



IMPREGNATION. 405 

than seven days unless impregnated, and if impregnation is to 
occur, it must take place within the first week after ovulation. 
Since, therefore, ovulation and menstruation usually occur to- 
gether, and since impregnation probably occurs about the be- 
ginning of menstruation, we reckon from the first day of the last 
menstruation 280 days forward to determine the probable time 
of labor. This is equivalent to adding nine calendar months 
and seven days to the first day of the last menstrual period. 
It is evident that this calculation at best gives only the approxi- 
mate time. 

While fertilization probably occurs at the time mentioned, 
the spermatozoon effecting fecundation may have been in the 
female genital tract for weeks. Its vitality here is so prolonged 
that the time of its deposit with reference to menstruation very 
probably has little to do with whether or not conception shall 
occur. 

Impregnation. — The term impregnation, or fertilization, or 
fecundation, is used to signify that union of the male and female 
sexual cells which makes possible the development of a new 
human being. Normally impregnation takes place in the Fal- 
lopian tube, and almost always in the outer third. The male 
element, the spermatozoon, seeks and penetrates the female ele- 
ment, the ovum. It is the blending of the nuclei (pronuclei) 
which is essential. Spermatozoa in large numbers swarm around 
the ovum and several at least enter the perivitelline space. 
Only one, however, is destined usually to enter the ovum. As 
it approaches the vitelline membrane, head first, the protoplasm 
of the ovum swells up into a prominence to meet it. The fertiliz- 
ing spermatozoon makes its way through the vitelline membrane, 
losing its tail in the passage, and becomes the male pronucleus. 
The female pronucleus now advances from its central position to 
meet the male element, and they coalesce to become the segmen- 
tation nucleus. Impregnation has now taken place. The seg- 
mentation nucleus represents a new being. It contains anatom- 



406 REPRODUCTION. 

ical elements from both parents, and it is not surprising that the 
child should resemble both, anatomically and otherwise. 

The term " ovum " has so far been used to signify the unim- 
pregnated sexual cell discharged from the female ovary. It is 
also used to signify the fertilized cell, and is in fact often ap- 
plied without much precision to the product of conception at 
almost any stage of its intrauterine development. 

The fertilized ovum is carried through the tube to the uterus, 
arriving there some seven days after its fecundation. In its pas- 
sage it becomes covered with a coating of albuminous material. 
This layer is probably impervious to spermatozoa — which fact 
may account for the practical universality of fecundation in the 
outer part of the tube, if at all. The coating corresponds to the 
white of an egg, in that it penetrates the perivitelline membrane 
and furnishes nutritive material to the vitellus. On reaching the 
uterus the ovum becomes attached to and covered by the thick- 
ened mucous membrane of that organ in a way to be noted pres- 
ently. Here it remains until expelled during parturition. 

Segmentation. — As soon as union of male and female pro- 
nuclei has taken place, cleavage of the ovum begins. The 
nucleus (segmentation nucleus) and protoplasm divide by karyo- 
kinesis to form two nearly similar cells. These two divide 
into four, these four into eight and so on, till a large number of 
cells occupy the vitelline space and are all surrounded by the 
perivitelline membrane. As division proceeds, cells arrange 
themselves around others, so that the former occupy the cir- 
cumference and the latter the center of the vitelline cavity. 
Later, while the outer cells constitute a layer covering the entire 
inner surface of the perivitelline membrane, the inner cells group 
to form a mass which is in contact with the outer layer at one 
point only — like a ball lying in a relatively large hollow sphere. 
The space thus left between the two kinds of cells is called the 
segmentation cavity. Soon the surrounding cells become attenu- 
ated (Rauber's cells) and disappear. Their place, as a surround- 



SEGMENTATION. 



407 



ing envelope, is taken by some of the cells of the inner layer. This 
second surrounding layer is the epiblast, or ectoderm ; the sur- 
rounded mass is the hypoblast, or entoderm. 

Fig. 93. 






Sections of the Ovum of a Rabbit, Showing the Formation of the Blastoder- 
mic Vesicle. (From Yeo after E. Van Beneden.) 
a, b,c, d, are ova in successive stages of development; Z, p, zona pellucida ; ect, ecto- 
meres, or outer cells ; ent, entomeres, or inner cells. 

Before long the entoderm spreads out over a larger area, and 
from it and from the ectoderm is developed a layer of cells, the 
mesoblast, or mesoder?n, which occupies a position between the 



408 



REPRODUCTION. 



FlG. 94. 



other two layers. This three-layered germ is now the blasto- 
dermic vesicle, or the gastrula, and its cavity is the archentero?i, or 
celenteron. From these three germ layers are developed all the 
parts of the body by the formation of folds, ridges, constrictions, 
etc., and by various metamorphoses which have as their end 
the adaptation of structure to function. 

Derivatives of the Germ Layers. — According to Heisler 
these are : 

From the ectoderm : ( 1 ) The epidermis and its appendages, 
including the nails, the hair, the epithelium of the sebaceous 
and sweat glands and the epithelium of the mammary gland. 
(2) The infoldings of the epidermis, including the epithelium of 

the mouth and salivary glands, of 
the nasal tract and its communicat- 
ing cavities, of the external audi- 
tory canal, of the anus and anterior 
urethra, of the conjunctiva and 
anterior part of the cornea, the 
anterior lobe of the pituitary body, 
the crystalline lens and the enamel 
of the teeth. (3) The spinal cord 
and brain with its outgrowths, in- 
cluding the optic nerve, the retina 
and the posterior lobe of the pitu- 
itary body. (4) The epithelium 
of the internal ear. 

From the entoderm : The epi- 
thelium of the respiratory tract, 
of the digestive tract (from the 
back part of the pharynx to the 
anus, including its associated glands, the liver and pancreas), of 
the middle ear and Eustachian tube, of the thymus and thyroid 
bodies, of the bladder and first part of the male urethra and of 
the entire female urethra. 




Impregnated Egg, 
With commencement of formation of 
embryo ; showing the area germinativa 
or embryonic spot, the area pellucida, 
and the primitive groove and streak. 
{Kirkes after Dalton.) 



DEVELOPMENT OF MESODERM. 409 

From the mesoderm : ( 1 ) Connective tissue in all its forms, 
such as bone, dentine, cartilage, lymph, blood, fibrous and 
areolar tissue ; (2) muscular tissue; (3) all endothelial cells; 
(4) the spleen, kidney and ureter, testicle and its excretory ducts, 
ziterus, Fallopian tube, ovary and vagina. 

The Embryonal Area. — Soon after the germ reaches the 
uterus (probably) there appears on its surface an oval whitish 
spot, the embryonal ai-ea. The impregnated ovum is still in the 
shape of a vesicle. It is from the embryonal area alone that the 
body is developed. The other parts are accessory. Longitu- 
dinal division of this area is supposed to give rise to twins of the 
same sex and of almost identical structure. Running in the 
long diameter of the embryonal area is a marking, the primitive 
streak, in which is a longitudinal depression, the primitive groove. 
(Fig. 94.) These surface markings are caused by a thickening 
of the ectoderm. (Fig. 95.) 

Development of Mesoderm. — It is about this time that the 
mesoderm makes its appearance. It begins under the primitive 
groove and extends in all directions. It originates from both 
ectoderm and entoderm, and lies between them. In the median 
line the three layers are closely united to each other. (Fig. 
95.) At first the mesoderm does not completely embrace the 
germ, but is deficient opposite the embryonal area. 

Fig. 95 shows that the cells of the mesoderm make up a thick- 
ened mass near the median line, but farther away they constitute 
two distinct lamellae. The mass near the median line is the 
vertebral or axial plate. The outer of the lateral lamellae is the 
somatic mesoderni ; the inner is the splanchnic mesoderm. The 
ectoderm and somatic mesoderm unite to form the somato- 
pleure ; the entoderm and splanchnic mesoderm unite to 
form the splanchnopleure. The interval left between the so- 
matopleure and splanchnopleure is the celom, or body cavity. 
(Fig. 96.) The great serous cavities of the body are de- 
veloped from it. 



4io 



REPRODUCTION. 



Beginning Differentiation. — It thus appears that the embryo 
is beginning to develop from the simple vesicle into specialized 
parts. 




We shall notice briefly the development of the body proper, and 
the extra-embryonic accessory structures, the umbilical vesicle, 



THE NEURAL CANAL. 



411 



amnion, alla?itois and placenta. As regards the embryonic body, 
some of the most prominent occurrences connected with its de- 



■ o 




velopment consist in the formation of the neural canal, chorda 
dorsalis, or notochord, and mesoblastic somites. 

Neural Canal. — About the fourteenth day, along underneath 
the primitive groove, the cells of the ectoderm become thickened 



412 



REPRODUCTION. 



to form the medullary plate. The edges of this longitudinal 
plate soon begin to curl up, and thus form the medullary furrow, 
ox groove. (Fig. 96. ) The margins of the adjacent ectoderm are 
carried up with the curling edges, and constitute the medullary 
folds. Later the edges of the medullary plate meet each other, 
and join to form a closed canal, the 7ieural or medullary canal. 
The edges of the medullary folds unite above, so that the neural 

Fig. 97. 




Transverse Section through Dorsal Region of Embryo Chick (45 hours). 
One-half of the section is represented ; if completed it would extend as far to the left as to 
the right of the line of the medullary canal (Mc). A, epiblast ; C, hypoblast, consisting of a 
single layer of flattened cells ; Mc, medullary canal ; Pv, protovertebra ; Wd, Wolffian duct ; 
So, somatopleure ; Sfi, splanchnopleure ; fip, pleuroperitoneal cavity; ch, notochord ; ao, 
dorsal aorta, containing blood-cells ; v, blood-vessels of the yolk-sac. {Kirkes after Foster 
and Balfour.) 

canal comes to lie underneath the surface ectoderm. (Fig. 97.) 
The neural canal is the forerunner of the whole nervous 
system. 

Chorda Dorsalis. — The method of formation of the chorda 
dorsalis, or notochord, is very similar to that of the neural canal. 
It is a solid, instead of a cylindrical, longitudinal collection of 
cells, extending along the dorsal aspect of thecelom. It is de- 
veloped from the entoderm. A thickening of the cells of this 
layer constitutes the chordal plate. Its edges curl up in a direc- 
tion opposite to those of the medullary plate, and carry with them 



SOMITES AND BODY CAVITY. 413 

chordal folds of the entoderm. When the curling edges have joined 
to form a solid cylinder of cells, the chordal folds unite over the 
ventral surface of the cylinder. Figures 96 and 97 illustrate 
these facts. The notochord is in the line of the future vertebral 
bodies, but it is not developed into any adult structure. 

Somites. — These are masses of cells developed from the axial 
plates of the mesoderm, lying parallel with and on each side of 
the notochord. (Fig. 97.) They are in segments, the formation 
of which begins in the neck and proceeds caudad and cephalad. 
They are sometimes called the protovertebrce. They represent 
the primitive vertebrae. 

The body begins to assume shape and the fetal appendages to 
be developed at the same time. The latter are for the protec- 
tion and nutrition of the embryo. The essential parts of a verte- 
brate are a vertebral column with a neural canal above and a body 
cavity below it. The body cavity contains the alimentary canal. 
The somites representing the vertebral column and the formation 
of the neural canal have been noticed. 

Body Cavity. — At first the embryo, as represented by the 
embryonal area, is on a level with the remaining surface of the 
blastoderm. Soon, however, there appears, marking the head 
of the embryo and with its concavity backward, a crescentic 
folding-in of the blastodermic wall. It is evident on the surface 
as a simple furrow. This tucking-in finally surrounds the whole 
embryonal area, and the surface fissure, now oval, becomes 
deeper and deeper, until those portions of the wall which are be- 
ing tucked under the embryo approach each other on its ventral 
aspect and divide the yolk into two communicating cavities. 
(See Figs. 99 and 100.) 

The layers of the blastoderm thus folded underneath the em- 
bryo are the visceral plates. They form the boundaries of a cav- 
ity which still communicates in front, at the site of the future 
umbilicus, with the yolk-sac. This narrow canal is the vitelline 
duct, and the two cavities communicating through the vitelline 



414 



REPRODUCTION. 



duct are the future ali??ie?itary canal and the yolk-sac, or umbilical 
vesicle. It is to be noticed that the visceral plates embrace both 
somatopleure and splanchnopleure, and that it is the ectodermic 



Fig. 98. 



aS*± 



Lfiflj* 




Diagrammatic Section showing the Relation in a Mammal between the 
Primitive Alimentary Canal and the Membrane of the Ovum. 

The stage represented in this diagram corresponds to that of the fifteenth or seventeenth 
day in the human embryo, previous to the expansion of the allantois ; c, the villous chorion ; 
a y the amnion ; a' , the place of convergence of the amnion and reflexion of the false amnion; 
a" a" ', outer or corneous layer ; e, the head and trunk of the embryo, comprising the 
primitive vertebrae and cerebro-spinal axis ; z\ i, the simple alimentary canal in its upper and 
lower portions. Immediately beneath the right hand i is seen the fetal heart, lying in the 
anterior part of the pleuroperitoneal cavity ; v, the yolk-sac or umbilical vesicle ; vi, the 
vitello-intestinal opening; u, the allantois connected by a pedicle with the hinder portion of 
the alimentary canal. (Kirkes after Quain.) 

layers of the splanchnopleure which finally join to form the gut 
tract, and the somatopleure which forms the ventral and lateral 
walls of the body cavity. The gut tract has the shape of a 



THE FETAL MEMBRANES. 415 

straight tube occupying the long axis of the embryo and open- 
ing into the umbilical vesicle. 

Fetal Membranes. 
Umbilical Vesicle. — The umbilical vesicle represents that 
part of the vitellus which has not been constricted off to form 
the gut tract. (Figs. 98, 99, 100.) It furnishes nutriment 
to the embryo for a short time and is then largely cut off from 
the body. It gradually shrivels (Figs. 104, 105), and with 

Figs. 99 and 100. 




a, chorion with villi. The villi are shown to be best developed in the part of the chorion to 
which the allantois is extending ; this portion ultimately becomes the placenta ; b, space be- 
tween the true and false amnion; c, amniotic cavity; d, situation of the intestine, showing 
its connection with the umbilical vesicle; e, umbilical vesicle; f, situation of heart and ves- 
sels ; g, allantois. {Kirkes.) 

that part of the duct external to the abdomen is cast off either 
before or at parturition. Vessels develop in its walls and ab- 
sorb the nourishment in it to be conveyed to the embryo. But 
in the human being more satisfactory arrangements for nutrition 
are soon made and its function ceases. 

Amnion. — When the embryo has become depressed, as it were, 
into the substance of the blastoderm, and while the body cavity 
is being formed, the layers of the somatopleure grow up over the 
embryo to meet and blend dorsally. (Figs. 104, 105.) The 



416 



REPRODUCTION. 



two layers of which the somatopleure is composed separate, the 
outer forming the false amnion and the inner the true amnion. 
The false amnion now coalesces with the original vitelline mem- 
brane to constitute the false chorion. Evidently there is thus 



Figs, ioi and 102. 





Diagram of Fecundated 
Egg. 

a, umbilical vesicle ; b, 
amniotic cavity ; c, allan- 
tois. {Kirkes after Dal- 
ton.) 



Fecundated Egg with Allantois Nearly Complete. 
a, inner layer of amniotic fold ; b, outer layer of ditto ; 
c, point where the amniotic folds come in contact. The 
allantois is seen penetrating between the outer and inner 
layers of the amniotic folds. This figure, which represents 
only the amniotic folds and the parts within them, should 
be compared with figs. 99, 100, in which will be found 
the structures external to these folds. ( Kirkes after Dalton. ) 



formed a closed cavity, the amniotic cavity, between the true am- 
nion and the body of the embryo. 

At first the amnion and the embryo are in close contact, but 
soon the cavity begins to be distended with a fluid, the liquor 
amnii, which increases until it reaches a considerable quantity. 
It affords mechanical protection to the fetus during intrauter- 
ine life, and at labor serves to evenly dilate the cervix. When 
this has been accomplished is the usual time at which the sac rup- 
tures and the liquor amnii escapes. It also supplies the fetal 
tissues with water, parts of it being swallowed from time to 
time. 

The cavity between the false amnion and the true amnion is 
continuous, with the body cavity at the umbilicus. 

Allantois. — The allantois grows out from the back part of the 
intestinal canal into the celom or the body cavity. (Figs, ioi, 



THE ALLANTOIS. 



417 



102. ) It is of splanchnopleuric origin. It soon becomes a mem- 
branous sac, the walls of which are very vascular. It fills the 
space between the two amniotic folds and joins the false amnion. 
Its vessels thus reach the chorion, which is already establishing 

Fig. 103. 




-H-HBP 



-vt 



xt 




-W 



This and the two following wood-cuts are Diagrammatic Views of Sections, 
through the developing ovum, showing the formation of the mem- 
BRANES of the Chick. ( Yeo, after Foster and Balfour.) 
A, B, C, D, E, and F, are vertical sections in the long axis of the embryo at different 
periods, showing the stages of development of the amnion and of the yolk-sac ; I, II, III, and 
IV, are transverse sections at about the same stages of development ; i, ii, and iii, give only 
the posterior part of the longitudinal section to show three stages in the formation of the al- 
lantois ; e, embryo ; y, yolk ; p>p, pleuroperitoneal fissure ; vt, vitelline membrane ; of, am- 
niotic fold ; al, allantois. 

vascular connections with the mother. Finally they are distrib- 
uted only to a certain part (placenta) of the chorion ; and 
as the allantoic vessels anastomose more and more freely with 
those of the chorion, the umbilical vesicle shrivels, as it is no 
27 



4i8 



REPRODUCTION. 



longer needed. The vessels of the allantois are the two allan- 
toic arteries and the same number of allantoic veins. The al- 
lantois also receives the fetal urine. 

As the true placental circulation is established and the vis- 
ceral plates close the abdominal cavity, the allantois is constricted 
at the umbilicus so as to be divided into two parts. That 

Fig. 104. 



PP-lf^- 






e> embryo; a, amnion ; a' , alimentary canal ; vt % vitelline membrane; af, amniotic fold ; 
ac, amniotic cavity ; y, yolk ; al y allantois. 



THE CHORION. 



419 



outside the body shrivels and is cut away with the umbilical 
cord at birth, while that inside the body becomes the first part 
of the male and the whole of the female urethra, the bladder 
and the urachus. 

Chorion. — The chorion is the outer surrounding membrane of 
the embryo after the appearance of the amnion. It consists of 



Fig. 105. 




Diagrammatic Sections of an Embryo. 

Showing the destiny of the yolk-sac, ys. vt, vitelline membrane ; fifi, pleuroperitoneal 
cavity ; ac, cavity of the amnion ; a, amnion ; a' , alimentary canal ; ys, yolk-sac. 

three layers. From without inward these are the original vitel- 
line membrane, the false amnion and the allantois. The allan- 
tois has been seen to extend around between the two amniotic 
folds and to blend with the outer. From its formation from 
these several membranes, the chorion evidently consists of the 
outer ectodermic, inner entodermic and intervening mesodermic 
strata. 



420 REPRODUCTION. 

By the time the impregnated ovum reaches the uterus, the 
chorion (false at this time) has numerous spike-like projections, 
— villi — over its whole surface. (Fig. 98.) These are at first 
non -vascular, but soon become vascular by the projection into them 
of capillaries from the vessels of the allantois. These capillaries 
probably absorb nutrient matter secreted by the uterine glands. 
But at the beginning of the third month the villi become much 
more highly developed over a certain part of the surface of the 
chorion than at other points, and a more intimate relation is estab- 
lished between their vessels and those of the mother ; here the 
placenta is to be formed. 

The Decidua. — The decidua of pregnancy consists of the hyper- 
trophied mucous membrane lining the cavity of the uterus and 
reflected at a certain point entirely over the developing ovum. 
Before the ovum reaches the uterus, the mucous membrane of 
the latter has been undergoing changes, such are mentioned under 
Menstruation. If fecundation has not taken place, menstruation 
occurs and the mucosa is discharged under the name of the decidua 
menstrualis. But if conception has occurred, menstruation does 
not ensue and the uterine mucosa becomes much more thick and 
spongy. Whether or not it shall be discharged as the decidua 
of menstruation or be retained to form the decidua of pregnancy 
is probably a point which is decided while the ovum is yet in 
the tube. 

When the fecundated ovum reaches the uterus it becomes at- 
tached to the mucous membrane, usually a little to one side of 
the median line on the posterior wall. The mucous membrane 
extends over and completely envelops it. This reflected portion 
is the decidua reflexa ; that lining the whole uterine cavity is the 
decidua vera, while that part of the decidua vera intervening be- 
tween the ovum and the uterine wall is the decidua serotina and 
becomes the maternal part of the placenta. 

Of course there is at first a considerable cavity left between 
the reflexa and the vera, but as the embryo increases in size the 



THE PLACENTA. 42 I 

space becomes smaller and is obliterated by the end of the fifth 
month. After this time both vera and reflexa undergo retro- 
grade changes due to pressure and become closely attached to 
the chorion. They are discharged with the membranes at birth. 
Placenta. — The placenta is the organ of nutrition for the 

Fig. 106. 




Diagrammatic View of a Vertical Transverse Section of the Uterus at the 
Seventh or Eighth Week of Pregnancy. 
c, c, c' , cavity of uterus, which becomes the cavity of the decidua, opening at c, c, the cor- 
nua, into the Fallopian tubes, and at c' into the cavity of the cervix, which is closed by a 
plug of mucus ; dv, decidua vera ; dr, decidua reflexa, with the sparser villi imbedded in its 
substance ; ds, decidua serotina, involving the more developed chorionic villi of the com- 
mencing placenta. The fetus in seen lying in the amniotic sac ; passing up from the um- 
bilicus is seen the umbilical cord and its vessels passing to their distribution in the villi of the 
chorion ; also the pedicle of the yolk-sac, which lies in the cavity between the amnion and 
chorion. (Kirkes after Allen Thomson.} 



42 2 REPRODUCTION. 

fetus after about the end of the third month. Through it the ves- 
sels of the fetus and those of the mother are brought into most 
intimate relations. 

It has been said that the villi of the chorion in one locality be- 
come very highly developed. This is at the site of the reflec- 
tion of the decidua serotina and is the chorion frondosum. The 
union of these, with certain other developments, constitutes the 
placenta. 

The decidua serotina becomes very spongy. It is filled with 
sinuses, into which the enlarged villi of the chorion frondosum 
project. The sinuses are filled with maternal blood, while the 
capillaries of the villi contain fetal blood. There is no direct 
co?inection between the vessels of mother and child, but the 
thin lining of the villi and sinuses allows free interchange of 
materials by osmosis. 

It seems that the interchange is under the influence of two sets 
of cells, each disposed in a single layer — one belonging to the 
maternal and the other to the fetal part of the placenta. 
These layers of cells are situated on either side of the membrane 
of the villus. They seem to take out of the maternal blood 
materials needed for the nutrition of the fetus, and out of the 
fetal blood materials which require removal. The maternal 
blood performs both alimentary and respiratory functions for the 
fetus. 

The placenta as a whole is discoid in shape. Its fetal surface 
is concave and covered by the amnion. The mass has a diame- 
ter of 4-5 in., and a thickness of half an inch. The villi re- 
ceive blood from the allantoic or umbilical arteries ; it is returned 
by the umbilical vein. 

At labor uterine contractions detach the placenta and the 
decidua and expel them from the womb. The separation 
takes place in the deeper part of the maternal placenta, or 
decidua serotina, so that the mass discharged represents both 
the fetal and maternal portions. The vessels entering the 



THE UMBILICAL CORD. 423 

sinuses do so obliquely ; consequently uterine contractions at 
birth very effectually check the hemorrhage which separation 
of the placenta occasions. 

Umbilical Cord. — The umbilical cord is made up of the ves- 
sels which convey blood between the placenta and fetus, to- 
gether with the remnants of the umbilical vesicle and allantoic 
stalk, all of which are held together by the jelly of Wharton, a 
species of connective tissue. 

The outgrowing allantois has developed in it the two allantoic 
arteries and veins. By the time the placenta is formed the 
allantoic stalk has become much elongated, and the allantoic 
vessels extend into the fetal placenta (chorion frondosum) and 
become now the umbilical vessels. The two veins blend to con- 
stitute a single umbilical vein, but the arteries remain separate. 
The vein enters the fetal body at the umbilicus, passes to the 
under surface of the liver and divides in a manner to be noted 
presently. After birth the intra-abdominal portion atrophies, 
and is the round ligament of the liver. The two umbilical 
arteries issue at the umbilicus. Their intra-abdominal portions 
are the fetal hypogastric arteries. 

The average length of the umbilical cord is about twenty-one 
inches. It appears to be twisted on account of the spiral course 
of its relatively long arteries. It is usually attached near the 
center of the fetal surface of the placenta. 

Condition of the Fetal Membranes at Birth. — The mem- 
branes discharged with the placenta at birth are, from without 
inward, the decidua vera, decidua reflexa, chorion and a?nnio?t. 
The amniotic fluid, in which the fetus floats, reaches its maxi- 
mum amount at about the sixth month. It is sufficient then to 
force the amnion closely against the chorion, covered by the 
decidua reflexa ; these last named (chorion and reflexa) are in 
turn forced everywhere against the decidua vera. The result is 
that all four become practically one membrane, though the union 
between amnion and chorion is not so close as that between the 



424 REPRODUCTION. 

other layers. These membranes constitute, then, a sac filled 
with fluid. The sac is ruptured in labor, and the child escapes 
through the rent. Afterwards the decidua vera and placenta 
are detached, and escape together as the " after birth." 

Development of the Circulation. — The development of the 
circulation maybe considered in these stages: (i) Vitelline 
circulation, (2) placental circulation, (3) adult circulation. 
The heart is the propelling organ in all these. 

1. Vitelline Circulation. — The blood and vessels make their 
appearance almost as early as the primitive groove. Certain 
blastodermic cells are transformed into both red and white cor- 
puscles. They are larger than the adult's cells and both are 
nucleated. Blastodermic cells also group to form small tubes, 
which constitute the area vasculosa. At the same time meso- 
blastic cells develop two tubes, one along each side of the body, 
which soon unite to form a single one, representing the heart. 
It becomes enlarged and twisted upon itself, and pulsations 
begin in it at a very early date. The heart is in the median 
line and gives off two arches which unite below to form the 
abdominal aorta. From the arches pass branches to the area 
vasculosa, which now form a nearly circular plexus around the 
embryo. Two of these branches, larger than the others, enter 
the umbilical vesicle and become the omphalomesenteric arteries ; 
there are two corresponding veins. This circulation through 
the omphalo-mesenteric vessels and the area vasculosa does not 
continue long in the human being. As soon as the allantois is 
formed and the placental circulation begins to be set up, the 
omphalo-mesenteric vessels are obliterated and the place of the 
first circulation is taken by the second. 

Development of the Heart. — The tube just mentioned as rep- 
resenting the heart has communicating with it two veins at its 
lower extremity and two arteries at its upper. Soon the tube 
becomes twisted upon itself so that the upper (arterial) is thrown 
in front of the lower (venous). The loop is V-shaped and is 



THE PLACENTAL CIRCULATION. 425 

the outline of the future ventricles. Afterward a constriction 
forms the auricle. At this time the heart consists of a single 
ventricle and a single auricle. Later the ventricular and auric- 
ular septa are formed. The latter appears after the former and 
is incomplete ; the opening left between the auricles is the fora- 
men ovale. 

2. Placental Circulation. — As the allantois is developed and 
the vitelline circulation is abolished, the hypogastric arteries are 
given off first from the aorta, but later (with the development 
of the vessels of the lower extremities) they are' pushed down, 
as it were, so that they take origin from the internal iliacs. 
They pass to the umbilicus and thence to the placenta by the 
cord. Blood is at first returned from the placenta by tw T o um- 
bilical veins, but these soon fuse into one. 

Object of Placental Circulation. — Since the activity of the 
respiratory and alimentary tracts has not been established, their 
functions must be performed by those of the mother and the 
necessary materials supplied from her blood. Consequently 
there must be a continual passage of fetal blood to and from the 
placenta to discharge effete matter and to absorb nutriment. 
Certain modifications of the circulatory apparatus, not requisite 
after birth, are necessary to bring this about. 

Course of Fetal Circulation, — The umbilical vein containing 
blood enriched with oxygen and other materials enters the body 
at the umbilicus and passes to the under surface of the liver. 
Here it divides into two branches. The larger joins the portal 
vein and enters the liver ; the smaller is the ductus venostis, 
which enters the ascending vena cava. 

The ascending vena cava, when it enters the right auricle, 
therefore, contains blood from the lower extremities, blood 
which has come from the placenta directly through the ductus 
venosus, and blood which has come from the placenta indirectly 
through the liver. Considering that blood from the body of the 
fetus is venous and that blood directly from the placenta is arte- 



426 



REPRODUCTION. 



rial, the contents of the ascending vena cava are mixed when they 
enter the heart. The Eustachian valve, together with the direc- 

Fig. 107. 




Diagram illustrating the Circulation through the Heart and thb principal 
Vessels of a Fetus. (From Yeo after Cleland.) 

a, umbilical vein ; &, ductus venosus ; f, portal vein ; e, vessels to the viscera ; d, hypo- 
gastric arteries ; c, ductus arteriosus. 



Hon of the entering current, causes the blood from the ascending 
vena cava to pass through the foramen ovale into the left auricle. 



THE PLACENTAL CIRCULATION. 427 

Blood from the upper extremities (impure) enters the right 
auricle through the descending vena cava. The Eustachian 
valve and the direction of the current here again cause this blood 
to enter the right ventricle. There is supposed to be very little 
mingling of blood from the two venae cavae as it passes thus through 
the right auricle. At the same time the blood which has entered 
the left auricle through the foramen ovale, augmented slightly 
by blood from the ill -developed pulmonary veins, passes into 
the left ventricle. The ventricles now contract simultaneously. 

Blood from the right ventricle (impure) passes in small part 
through the pulmonary artery to the lungs, but chiefly through 
a tube, the ductus arteriosus, into the descending part of the 
aortic arch. 

Blood from the left ventricle (mixed) enters the aorta and goes 
to the system at large. 

The vessels going to the head and upper extremities are given 
off from the aortic arch before it is joined by the ductus arteriosus. 
Since the ductus arteriosus contains impure blood, the supply 
going to the upper extremities is purer than that going to the 
lower. 

Of the blood which passes down the aorta a part leaves by the 
hypogastric arteries, to go again to the placenta, while the other 
part is distributed to the trunk and lower extremities. 

It thus appears that the liver is the only organ of the fetus 
which receives pure blood, and that the head and upper extrem- 
ities are better provided for in this respect than are the lower 
parts. This may account for the relatively large liver of the 
fetus, and for the fact that the upper extremities are better devel- 
oped than the lower. 

The ductus arteriosus, ductus venosus, foramen ovale, Eustachian 
valve, hypogastric {umbilical) arteries and the umbilical vein are 
the organs which distinguish the placental circulation, and they 
all partially disappear after birth, as will be immediately seen. 

3. Adult Circulation. — The circulation as it exists in the adult 



428 REPRODUCTION. 

has been described. It is only necessary to see what changes 
mark its establishment. 

When the child is born detachment of the placenta, or ligation 
of the cord, stops the placental circulation. The first noticeable 
effect comes from the consequent deoxygenation of the blood. 
The respiratory center is stimulated and the child gasps to fill 
the hitherto collapsed lungs with air. Owing to the diminished 
resistance in the expanded lungs, the pulmonary artery begins 
to carry most of the blood from the right ventricle, and the 
ductus arteriosus commences to atrophy. Before birth, too, the 
Eustachian valve becomes less distinct and the foramen ovale 
partly closes. At labor a kind of valve guards the opening of 
the foramen ovale and allows the escape possibly of a little 
blood from the right into the left auricle, but none in the oppo- 
site direction. It commonly closes about the tenth day of ex- 
trauterine life. The ductus arteriosus is reduced to the condi- 
tion of an impervious fibrous cord between the third and tenth 
days after birth. 

The hypogastric arteries, umbilical vein and ductus venosus 
are closed between the second and fourth days. That part of 
each hypogastric artery between the internal iliac and the upper 
lateral part of the bladder remains in adult life as the superior 
vesical artery \ the part between this point and the umbilicus is 
that which atrophies. The umbilical vein remains as the round 
ligament of the liver. The ductus venosus is represented by a 
fibrous cord in the fissure for the ductus venosus in the liver. 

The Skeleton. — The appearance of the notochord and of the 
protovertebrae, or somites, has been observed. The notochord 
becomes a thin line of soft cartilage, around which the bodies 
of the vertebra are developed, though it does not itself become 
those bodies. The protovertebrse were seen to lie longitudi- 
nally on either side of the notochord. These grow around the 
neural canal dorsally and the notochord ventrally to form the 
vertebrae. From them also are developed the muscles and skin 
of the back. 



DEVELOPMENT OF DIFFERENT ORGANS. 429 

The cranium is developed as a modification of the vertebral 
column. 

All the bones are in early fetal life cartilaginous or membra- 
nous. Centers of ossification appear at one or more points in 
each bone. 

The bones of the extremities are not at first separate. They 
bud out from the upper and lower parts of the trunk, to be sub- 
divided later. 

Nervous System. — The origin of the nervous system has 
been indicated in describing the neural canal. The mesodermic 
cells multiply and fill the tube, until only the canal of the spinal 
cord is left. Headward the neural canal terminates in a dilated 
extremity, which soon becomes divided into three vesicles, an- 
terior, middle and posterior. From these are developed the dif- 
ferent parts of brain. Some of these parts develop much more 
rapidly than others, and we thus account for the predominant 
size of the cerebrum. At first there are no cerebral convolu- 
tions, but later the cavity of the cranium seems too small for the 
brain and the characteristic infoldings occur. 

The eye is formed by the projection of the optic vesicle from 
the side of the anterior brain vesicle. 

The internal ear is formed by the projection of the auditory 
vesicle from the posterior brain vesicle. 

The alimentary canal is formed by being pinched off from 
the mesodermic layer of splanchnopleure. It communicates for 
some time by means of the vitelline duct with the umbilical 
vesicle. When cut off from the latter it is a straight tube, oc- 
cupying the long axis of the body just in front of the vertebral 
column, and is divided into the foregut, hindgut and a central 
part. Later it communicates above with the pharynx and mouth 
and opens below upon the external body surface (anus). The 
liver and pancreas are developed from protrusions from the sides 
of the duodenum. 

The bladder has been seen to be that part of the allantois 
which is constricted off and remains in the body. 



430 REPRODUCTION. 

The lungs are developed from the esophagus and at first lie 
in the abdominal cavity ; but the formation of the diaphragm 
fixes them in the thorax. 

The kidneys are developed from the Wolffian bodies. These 
bodies are embryonic structures only. Each is a tube lying 
parallel to the vertebral column on either side of it. This tube 
consists of a collection of tubules, which unite to forma common 
excretory duct. This duct joins the corresponding one from the 
opposite side to empty into the alimentary canal opposite the 
allantoic stalk. Outside the Wolffian bodies are two other ducts, 
the ducts of Miiller. They also enter the intestine. 

The Wolffian body finally gives place to the kidney, from 
which the ureter is developed. 

In the female the ducts of Miiller become the tube, uterus and 
vagina. In the male they atrophy. 

Just behind the Wolffian bodies are developed the ovaries or 
the testes, as the case may be. 



The development of a few of the organs has thus been simply 
referred to. 

Satisfactory explanation of these procedures can be given 
only in extended works on embryology, and this section may be 
closed with the subjoined table of development, which is ab- 
breviated from one by Heisler : 

First Week. — Segmentation and passage of ovum to uterus. 

Second Week. — Ovum in uterus. Decidua reflexa present. 
Entoderm and ectoderm layers formed — also mesoderm. Em- 
bryonal area, primitive streak in primitive groove. Chorion and 
villi. Amnion folds. Umbilical vesicle partly formed. Vas- 
cular area. Two primitive heart tubes. Gut tract partly formed. 

Third Week. — Body indicated. Dorsal outline concave. 
Vitelline duct. Amnion. Allantoic stalk. Visceral arches. 



FETAL DEVELOPMENT. 43 1 

Heart divides. Vitelline circulation begins. Gut tract still 
connected with umbilical vesicle. Liver evagination begins. 
Anal plate. Pulmonary protrusion. Wolffian bodies. Neural 
canal. The brain vesicles. Optic and otic vesicles. Olfac- 
tory plates. Notochord. 

Fourth Week. — Flexion of body. Yolk-sac largest size. 
Somites well formed. Allantois grows. Vitelline circulation 
complete. Allantoic vessels developing. Pharynx, esophagus, 
stomach and intestine differentiated. Pancreas begins. Pul- 
monary protrusion bifurcates. Ventral roots of spinal nerves. 
Limb buds apparent. 

Fifth Week. — Umbilical vesicle begins to shrink. Cord 
longer and spiral. Length of fetus two-fifths of an inch. Primi- 
tive aorta divides into aorta and pulmonary artery. Intestine 
shows loops. Bronchi divided. Ducts of Mliller. Epidermis. 
Olfactory lobe. Eyes move forward. Limb buds segment. 
Digitation indicated. 

Sixth Week. — Umbilical vesicle shrunken. Amnion larger. 
Vitelline circulation supplanted by allantoic. Teeth indicated. 
Duodenum, cecum. Rectum. Larynx. Genital folds and ridges. 
Dorsal roots of spinal nerves. Eyelids. Lower jaw and clavicle 
begin to ossify. Vertebrae and ribs cartilaginous. Fingers 
separate. 

Seventh Week. — Body and limbs well defined. Heart septa 
complete. Transverse and descending colon. Nails indicated. 
Cerebellum indicated. Muscles recognizable. Ossification in 
cranium and vertebrae begins. 

Eighth Week. — Head somewhat elevated. Parotid gland. 
Gall bladder. Miillerian ducts unite. Genital groove. Mam- 
mary glands begin. Sympathetic nerves. Nose discernible. Ad- 
ditional centers of ossification. 

Ninth Week. — Weight, three-fourths of an ounce. Length, 
one and a quarter inches. Pericardium. Anal canal. External 
genitals begin to indicate sex. Ovary and testis distinguishable. 
Kidney characteristic. External ear indicated. 



432 REPRODUCTION. 

Third Month. — Weight, four ounces. Length, two and three 
quarter inches. Chorion frondosum. Placental vessels. Ton- 
sil. Stomach rotates. Vermiform appendix. Liver large. 
Epiglottis. Ovaries descend. Testes in false pelvis. Hair 
and nails. Development of different parts of brain. Limbs 
have definite shape. 

Fourth Month. — Weight, seven and three-quarter ounces. 
Length, five inches. Head one-fourth of entire body. Germs 
of permanent teeth. Distinction of external genitals well marked. 
Spinal cord ends at end of coccyx. Eye-lids and nostrils closed. 

Sixth Month. — Weight, two pounds. Length, twelve inches. 
Amnion at maximum size. Trypsin in pancreatic secretion. 
Air vesicles. Eye-lashes. Lobule of ear characteristic. 

Seventh Month. — Weight, three pounds. Length, fourteen 
inches. Meconium. Ascending colon. Testes at internal rings. 
Cerebral convolutions evident. Differentiation of muscular 
tissue. 

Eighth Month. — Weight, four to five pounds. Length, six- 
teen inches. Body more plump. Ascending colon larger. 
Testes in inguinal canal. Skin brighter color. Nails project 
beyond finger tips. 

Ninth Month. — Weight, six to seven pounds. Length, twenty 
inches. Meconium dark green. Testes in scrotum. Labia 
majora in contact. Spinal cord ends at last lumbar vertebra. 
Ossification centers completed. 



INDEX. 



Abducens nerve 354 

Absorption . . . .122 

conditions influencing in 

body 126 

from alimentary canal . .127 

resume of 130 

Accommodation, ocular .... 383 



Adenoid tissue 37 

Adipose tissue 37 

formation of ...... . 264 

value of 264 

Adrenal glands $3 

Afferent nerves . 296 

Air, amount necessary .... 225 
alterations of in lungs . . .214 

cells 201 

composition of 212 

diffusion of in lungs . . . .212 

vesicles 201 

Albuminoids 24, 261 

Allantois 416 

Alveoli, capacity of 212 

Ammonia compounds antecedents 

of urea ... 246 

Amnion, the 415 

Amniotic cavity 415 

Amylopsin 1 14 

Animal heat 270 

loss of by evaporation . 274 

radiation of 274 

relation of to force , ,270 

source of 270 

specific 272 

total 272 

Antehelix 387 

Anterior chamber of eye . . . .381 

elastic lamella 379 

fundamental fasciculus . .310 
radicular zone . . . . . .310 

Apex beat 142 

28 433 



Aphasia .... 338 

Aqueous humor 382 

Arachnoid 305 

Archenteron 408 

Areolar tissue 37 

Arteria centralis retinae . . . .381 

Arterial circulation 157 

objects of 157 

rapidity of 169 

tension 162 

causes of 163 

conditions influencing . 165 

effect of respiration on . 227 

in different vessels . .165 

Arteries, contractility of. P . 1 61 

divisions of 158 

elasticity of 160 

structure of 158 

Arterioles 171 

Arytenoid cartilages . . . 197, 393 

Asphyxia 226 

Auditory canal, external .... 387 

center 338 

nerve 357 

terminations of . . . 390 

Auerbach, plexus of 1 10 

Auricle, left 137 

right .... 134 

Auricles, functions of 153 

Axis cylinders 280, 283 



Bacteria in digestion 119 

Bartholin's duct ... ... 56 

Bellini, straight tubes of . . . 240 

Bertin, columns of 238 

Bile ducts 73 

Bile, in digestion 114 

functions of 1 15 

properties and composition of 75 
Bilirubin 76 



434 



INDEX. 



Binary proximate principles . . 19 

Binocular vision 385 

Bladder 250 

absorption from 250 

structure of 250 

Blastoderm 408 

Blood, the ... 179 

alterations of in lungs . . .221 
amount in body . . . 179 

arterialization of ... . 221 

coagulation of 187 

color of .... 222 

composition of . . . . . .185 

functions of 179 

histological elements of . ,180 

plasma . .... 185 

composition of . . . .186 

platelets 185 

properties of 179 

serum 188 

Bone ... 40 

development of 41 

Bone marrow . 41 

Bowman's capsule 239 

Brain, the 319 

membranes of 304 

Breathing (see Respiration). 
Broca's convolution ..... 339 

Bronchi 200 

capacity of . 212 

Bronchioles ...... 201 

Burdach, columns of . . . 310, 315 

C. 

Calcium salts ....... 22 

Capillaries, the 169 

capacityof , 170 

pressure in . 173 

Capillary circulation 169 

causes of ... . . . 172 

rate of 172 

Carbohydrates . . . . 23, 88 

final products of ... 202 

value of in nutrition 262 

Carbon, amount in excreta . 268 

dioxide, amount exhaled . . 218 

amount in blood . . .221 

condition of in blood .219 

discharge of 215 

entrance of ... 223 

gain of in lungs . . .215 



Carbon, dioxide, inhalation of . 225 

interchange of in lungs 220 

source of exhaled . . .218 

monoxide, inhalation of . . 225 

Cardiac cycle 146 

length of 148 

occurrences during . . 147 

Cartilage 38 

hyaline 38 

white fibrous 40 

yellow elastic 39 

Cauda equina 306 

Celenteron 408 

Celom ... 413 

Cells . 27 

properties of ......... . 29 

structure of 28 

wandering . . 35 

Centrifugal nerves 295 

Centripetal nerves , 299 

Cerebellum, the . . ..... 342 

anatomy of 342 

fibers of 343 

function of 343 

peduncles of ...... . 343 

Cerebral localization 353 

Cerebro-spinal axis . .... 304 

system 280 

Cerebrum, the 328 

cells of 332 

convolutions of 332 

fibers of 332 

fissures of 330 

functions of 339 

lobes of . 329 

motor centers in 337 

paths from . . . 332, 337 

sensory centers in 338 

paths to 338 

special centers in .... . ^S 

Cerumen ... 81 

Cervical ganglia 367 

Cholesterin . . ...... 76 

Chorda dorsalis 412 

tympani .... 352, 355, 357 

Chordal folds . 413 

plates 412 

Chorion ....... 419 

frondosum 422 

Choroid coat of eye 379 

Chyme 109 



INDEX. 



435 



Ciliary muscle 380 

processes 380 

Circulation, the 131 

mechanism of 132 

pulmonic 13 1 

rapidity of 176 

systemic . ...... 131 

Circumvallate papillae .... 385 

Claustrum 327 

Cochlea 389, 391 

Colloids . . 123 

Colon 117 

Common bile duct 74 

Complemental air 211 

Conjunctiva 379 

Connective tissue 35 

Contractility of arteries . . . .161 

Convoluted tubules 240 

Cornea 379 

Corona radiata . 327 

Coronary valve 136 

Corpora Arantii 137 

quadrigemina 328 

striata 326 

Corpus luteum 400 

Corti, rods of 391 

Coughing 209 

Course of blood through heart . . 139 

Cranial nerves 344,364 

Creatin 248 

Cricoid cartilage ... 197, 393 

Crossed pyramidal tracts . . . .310 

Crura cerebri 324 

Crystalloids 123 

Cutaneous respiration 224 

sensations, center for ... 338 

Cutis vera 253 

Cystic duct 74 

D. 

Decidua menstrualis ...... 420 

of pregnancy 420 

Defecation 120 

Deglutition 95 

mechanism of 96 

nervous control of 97 

Dendrites 280, 286 

Descemet, membrane of . . . .379 

Descendens hypoglossi 363 

Dicrotic wave 168 

Diet, amount of 268 



Diet, determination of .... 267 
necessary constituents of . . 268 

Dietetics . . 267 

Diffusion in lungs . . . . .212 

Digestion . 89 

gastric 98 

intestinal 109 

object of 89 

pancreatic 113 

processes in . 91 

resume of 122 

Direct cerebellar tract 310 

Discus proligerus 400 

Dreams 370 

Ductus arteriosus 427, 428 

communis choledochus . . 74 

venosus 425, 428 

Dura mater 305 

E. 

Ear, the 386 

drum 388 

external . 386 

internal . 388 

middle 388 

Ectoderm 407, 408 

Efferent nerves 295 

Eighth nerve (see Auditory 
nerve). 

Elasticity of arteries 160 

functions of 161 

Electrical stimulation of nerves . 298 

Electrotonus 303 

Elementary tissues 31 

derivation of 31 

varieties of 31 

Elements in the body 17 

Eleventh nerve (see Spinal Ac- 
cessory). 

Embryonal area 409 

Encephalon (see Brain). 

Endocardium 133 

Endothelium 31 

Entoderm 407, 408 

Enzymes 90 

characteristics of 91 

classification of . . . . . . 90 

mode of action of 91 

Epiblast 407, 408 

Epidermis . 253 

Epiglottis 198 



43 6 



INDEX. 



Epinephrine . 84 

Epithelial tissue 31 

varieties of 32 

ciliated 33, 34 

columnar ^ 

glandular ....... 35 

modified 34 

neuro- ........ 35 

squamous 32 

stratified 32 

Esophagus 95 

Eupnea 225 

Eustachian valve 136 

Excretion 52, 235 

Expiration 207 

causes of 207 

forced 208 

effect of on blood -pressure .229 
Expired air, composition of . . .215 

External capsule 327 

Eye-ball, anatomy of 379 

movements of 377 

protection of 376 

F. 

Facial nerve 355 

Faradic current 299 

Fats, as foods 88 

end products of 263 

Fatty acids 24 

Fauces 95 

Feces, composition of . . . . .120 

Fecundation 405 

Ferrein, pyramids of 238 

Fertilization 405 

Fetal membranes 415, 423 

Fibrin 188 

factors 188 

ferment 188 

Fibrinogen 187, 188 

Fibrous tissue . . . ... 36 

Fifth nerve (see Trifacial). 

Filum terminale . . . . 305 

First nerve (see Olfactory). 

Foods . . 85 

classification of 86 

fate of in body 258 

how absorbed 128 

potential energy of . .271, 272 

where absorbed 130 

digested 122 



Foramina Thebesii 135 

Fourth nerve (see Patheticus). 

ventricle ... 321 

Fovea centralis 381, 382 

Fungiform papillae 386 

Funiculi graciles 321 

of Rolando . . .... 321 



of 



74 
154 
35° 
154 
154 
120 
108 

62 

65 

60 

60 

104 

102 



G. 

Gall bladder . . . 
Ganglion of Bidder 
of Gasser . . 
of Ludwig . . 
of Remak 
Gases in intestines 
Gastric digestion, resume 
glands, cells of 

nerve supply of 

structure of . 

varieties of . . 

juice, action of on foods 

properties and composi 

tion of 63, 

secretion of 63 

Gastrula 408 

Gelatinous tissue 37 

Glands 53 

adrenal 83 

agminate 112 

intestinal 65 

gastric 60 

mammary 81 

of Brunner 65, 112 

of Lieberkuhn .... 66, 112 

parotid 55 

salivary 55 

sebaceous 80 

secretion in 54 

solitary 112 

sublingual 55 

submaxillary 55 

sweat 254 

thyroid 82 

Glisson's capsule ... . . 70 

Glomeruli, renal 238 

Glossopharyngeal nerve . . . .357 

Glycocholic acid . 76 

Glycogen, formation of in liver . 77 
of influenced by vagus . 36 

Golgi, corpuscles of 29 

Goll, column of 31© 



INDEX. 



437 



Gustatory center 338 

Graafian follicles 398 

H. 
Hairs 253 

Haversian canals 40 

systems . .... 40 

Hawking 209 

Heart, anatomy of 132 

arrest of .... . 156 

capacity of 138 

causes of sounds of . . 149 

changes in shape of ... . 140 

contractions of 140 

development of 424 

diastole of 140 

force of . . .152 

histology of 138 

innervation of 153 

rate of 155 

sounds of ....... . 149 

systole of 140 

work of . 151 

Heat of body (see Animal heat). 

Hemoglobin 181 

Henle, loops of 240 

sheath of 284 

Hepatic artery 72 

Hiccough 209 

Hippuric acid 248 

Hunger, seat of 86 

Hydrocarbons 24 

Hydrochloric acid ...... 102 

Hydrogen, inhalation of . . . .225 

Hyperopia 384 

Hyperpnea . . . . 225 

Hypoblast 407 

Hypoglossal nerve 363 

Hypoxanthin 248 

I. 

lleo-cecal valve 118 

Impregnation 405 

Incus 388 

Induced currents 299 

Infundibula 201 

Innervation of vessels 177 

Inorganic foods 87 

Insalivation 93 

Inspiration 205 

causes of 205 



Inspiration, effect of on blood- 
pressure 228 

muscles of 206 

Inspired air, composition of . .215 

Interlobular veins 71 

Internal capsule ... . . 326 

respiration 195, 222 

Intestinal glands 65 

Intestine, digestion in 109 

divisions of ...... . 109 

movements of 116 

nerve supply of 116 

structure of .... 109 

Intralobular veins 70 

Intrapulmonary pressure . .210 
Intrathoracic pressure . . .210 
Iris, the 380 

K. 

! Kidney, blood supply of ... . 242 

structure of 235 

Kinetic energy .271 

Krause, end bulbs of 292 

L. 

! Labyrinth, bony 338 

membranous 390 

Lachrymal apparatus .... 377 

duct 377 

glands 377 

sac . 377 

Lactates, discharge of 248 

Lacteals 112 

Large intestine . . .... 117 

digestive changes in . .118 

divisions of 1 1 7 

movements of . . . .120 

structure of 118 

Larynx . . .... 197, 393 

nerve supply of 395 

I Laughing . . 209 

Lenticular ganglion . . . . 352 
Leucocytes (see White corpuscles). 
Lieberkuhn, crypts of . . . 66, 112 

Liquor amnii 416 

sanguinis (see Blood plasma) . 

Liver, anatomy of 69 

histology of 73 

lymphatics of 75 

nerve supply of 75 

vessels of 70 



43^ 



INDEX. 



Lumbar ganglia , 367 

Lungs 202 

capacity of 21 1 

Lymphatic glands £91 

Lymph 189 

course of 189 

flow of 193 

properties and composition of 19 1 
Lymph-vessels, origin of ... . 189 

M. 

Macula lutea 381 

Malleus 3S8 

Malpighian bodies 238 

pyramids 238 

Mammary glands 81 

Mastication 92 

Maturation 401 

Meckel's ganglion 353 

Medulla oblongata 319 

centers in 323 

functions of 322 

gray matter of . . . .321 

pyramids of 320 

relation of cord tracts to 322 

white fibers of . . . 321 

Meissner, corpuscles of . . 293 

plexus of no 

Membrana tympani 388 

Membranes, mucous 31 

serous ..... . 32 

Menstruation 403 

Mesoblast 407, 409 

Mesoderm 407, 409 

Metabolism 257 

conditions influencing . . . 265 
Micturition 251 

center for 251 

Milk, human 81 

Mitral valve 138 

Mixed lateral column . . . . 310 
Motor oculi communis 347 

paths from cerebrum . 332, 337 

Mucoid tissue 37 

Muscle fatigue . 50 

sense, center for 338 

Muscular contractions ..... 49 

tissues 42 

N. 
Nails, the 253 



Nasal duct 377 

Nerve cells ... .... 285 

centers 285 

fibers . . 281 

action of electricity upon 298 

afferent 296 

classification of ... . 294 
degeneration of ... . 308 
direction of currents in. 297 

efferent 295 

individuality of ... 285 

medullated 281 

non-medullated . . . 283 
properties of .... . 294 
rate of conduction in . 298 

terminals 289 

between epithelial cells 291 
in bulbs of Krause . . 292 
in Golgi's corpuscles . 294 

in glands 290 

in hair-follicles .... 290 
in Meissner' s corpuscles 293 
in Pacinian corpuscles . 291 
in plain muscle .... 290 
in striped muscle . . 289 
in tactile menisques . . 293 

trunks 283 

Nervous system, the 278 

development of ... . 429 
divisions of . . . . . 280 
general functions of . .278 

Neural canal 411 

Neuroglia 280 

Neurons . . . 280 

communication between 287 
Neutral fats . . . 24 
Ninth nerve (see Glossopharyn- 
geal). 
Nitrogen, amount necessary . . . 268 
Nitrogenous equilibrium . 260 
Nitrous oxide, inhalation of . 225 
Nutrition 257 

O. 

Olfactory bulb 345 

cells 375 

center ... 338 

nerve 345 

Olivary bodies . 320 

Omphalo-mesenteric vessels . . 424 
Ophthalmic ganglion 352 



INDEX. 



439 



Optic center 338 

commissure 346 

nerve 346 

thalami 326 

function of 327 

tracts . 346 

Organic and inorganic bodies . . 17 

Osmosis 123 

Otic ganglion 353 

Ova . . . 397 

Ovary, secretion of 84 

Ovulation 402 

Oxidation in the body . . . 258,271 
Oxygen, amount consumed • . .217 
amount in blood . . . 221 
condition of in blood . . . 221 
entrance of into tissues . . 223 
loss of in lungs 214 



P. 

Pacini, corpuscles of 

Pancreas, anatomy of 

histology of 

internal secretion of ... . 

nerve supply of 

secretion in 

Pancreatic juice ...... 

Paraglobulin 

Partial pressure of gases .... 
Patheticus nerve .... 

Pepsin 

Pepsinogen 

Peptones 

Pericardium 

Periosteum 

Perspiration 

Pfluger's law of contraction . . 

Pharynx 

Pia mater 

Pinna 

Pituitary body 

Placenta . 

Placental circulation 

Pneumogastric nerve 

influence of on respira 

tion . . . 

stomach and intes 



tines . . . 
Pons Varolii 

functions of . . . 
Posterior rchamber of eye . 



291 

66 

67 

68 

68 

68 

68 

187 

220 

348 

J 03 

61 

104 

*33 
40 

255 
302 

95 
305 
387 

84 
421 

425 
358 

361 

361 
323 
324 

38i 



Potassium salts 22 

Prehension 92 

Presbyopia 384 

Pronucleus, female 402 

male . . 405 

Proteids, as foods 87 

circulating 260 

final products of 259 

tissue 260 

Proteoses 104 

Protovertebrae , 413 

Proximate principles . ... 18 

classes of 19 

Ptyalin 94 

Pulse, the 166 

rate of 167 

varieties of 167 

tracings 168 

volume 151 

Pupil, the 380 

Q. 

Quaternary proximate principles . 24 

R. 

Ranvier, nodes of 282 

Rate of arterial current . . . .169 
Reaction of pupil .... 383, 384 

Receptaculum chyli 191 

Rectum 117 

Red corpuscles . 180 

chemical composition of 185 
development of . . . . 183 
fate of . ..... 183 

function of 181 

Reflex action 316 

Refraction, ocular 382 

Reil, island of 331 

Renal tubules 240 

Rennin 103 

Reproduction 396 

Reserve air 211 

Residual air 211 

Respiration . . . . 195 

abnormal 225 

afferent nerves of 232 

center for 231, '322 

costal 210 

cutaneous 224 

diaphragmatic 210 

effect of on blood -pressure . 227 



44o 



INDEX. 



Respiration, efferent nerves of . 233 

external 196 

influence of vagus on . . . 232 

internal 195, 222 

mechanism of 203 

modified 209 

nervous control of 230 

object of 195 

organs of 197 

rate of 209 

rhythm of 208, 231 

sounds of 209 

types of . . . 210 

Restiform bodies 320 

Retina! 381 

Rigor mortis 5 1 

Rolando, fissure of 330 

S. 

Saliva, functions of . . . . 93 
properties and composition 

of 57, 93 

Salivary glands 55 

histology of 56 

nerve supply of . . . . 57 
secretion in .... 59 

Schwann, sheath of 281 

white substance of . . . .281 

Sclerotic coat of eye 379 

Sebaceous glands 80 

Second nerve (see Optic nerve). 

Secretion 52 

external 54 

internal 54 

paralytic 59 

Segmentation 406 

cavity 406 

nucleus 405 

Semicircular canals .... 390, 391 

Semilunar valves 137, 138 

Sensations, common . ... 373 

special 374 

Senses, the 373 

Serum-albumin 187 

-globulin 187 

Seventh nerve (see Facial). 

Sighing 209 

Sight, sense of 376 

Sigmoid flexure 117 

Sinuses of Valsalva 137 

Sixth nerve (see Abducens). 



Skin, excretion by 251 

functions of 251 

structure of 253 

Sleep 369 

vascular phenomena of . . 370 

Smegma 81 

Smell, sense of ....... . 375 

Sneezing . . . • 209 

Snoring 209 

Sobbing 209 

Sodium salts 20 

functions of 21 

Solar plexus 367 

Somatopleure 409 

Somites 4^3 

Speech 394 

center 338 

Spermatozoa 396 

Spheno-palatine ganglion . . .353 

Spinal accessory nerve 362 

cord 305 

columns of 309 

commissures of ... . 306 
cross section of ... . 306 
degeneration in ... . 309 

functions of 316 

gray matter in ... . 307 
motor paths in . . . .312 
sensory paths in . . .313 
special centers in . . .319 
nerves ... .... 364 

Splanchnic nerves 367 

Splanchnopleure 409 

Starch 23 

Starvation, effects of 266 

Steapsin 114 

Stenson's duct 55 

Stercorin 120 

Still layer 172 

Stomach, the 98 

histology of 100 

movements of 106 

nervous supply of 108 

Straight tubules (renal) .... 240 

Striated muscle 42 

changes in form of . . 48 
characteristics of . . . 45 
chemical changes in . 47 
electrical changes in . . 47 
thermal changes in . . 48 
Stapes, the 388 



INDEX. 



441 



Sublobular veins 71 

Submaxillary ganglion 353 

Succus entericus 115 

Sugars 23 

Supplemental air 211 

Suspensory ligament 382 

Sweat glands 254 

Sweat, properties, composition of 255 

secretion of 255 

Sylvius, aqueduct of 321 

fissure of 330 

Sympathetic system . . 280, 366, 371 
Syntonin 104 

T. 

Tactile sensibility 374 

acuteness of 375 

Taste beakers 386 

sense of 385 

Taurocholic acid 76 

Temperature impressions .... 375 

of body 270 

Tenon, capsule of 377 

Tenth nerve ( see Pneumogastric ) . 
Ternary proximate principles . . 23 

Testes, secretion of 84 

Thermogenesis 270, 273 

Thermolysis 270, 274 

Thermotaxis 271, 275 

Third nerve (see Motor oculi com- 
munis). 

Thirst, seat of 86 

Thoracic duct 189 

ganglia 367 

Thorax 203 

Thyroid cartilage .... 197, 293 

gland 82 

Tidal air 211 

Touch, sense of 374 

Trachea 198 

Tragus 387 

Tricuspid valve 136 

Trifacial nerve . 349 

Trigeminal nerve 349 

Trypsin 113 

Turck, column of . 309 

Twelfth nerve (see Hypoglossal). 
Tympanum 388 

U. 

Umbilical cord ... s ... . 423 



Umbilical vesicle 415 

Urea 245 

daily discharge of 246 

formation of ..... 79, 246 

Ureters 250 

Uric acid . 247 

daily discharge of . . 248 

Urine, constituents of 245 

discharge of 249 

inorganic salts of 249 

properties of 245 

secretion of . 242 

variations in amount of . . 249 
in composition of . . . 249 

Uriniferous tubules 240 

secretory changes in . . 244 

V. 

Vaginal plexus 70 

Vagus nerve (see Pneumogastric). 

Valvulae conniventes no 

Vaso-motor nerves . . . .177, 368 

centers for 177 

Vater, corpuscles of 291 

Veins, capacity of 173 

current in 174 

pressure in 175 

structure of 174 

valves of 174 

Venous circulation 173 

causes of . . . 176 

Ventilation 224 

Ventricle, left . . 137 

right 136 

Venules * . . 171 

Vermiform appendix 117 

Vestibule of ear 388 

Villi in 

Vital force .... 12 

Vitelline circulation 424 

duct 413 

Vitreous humor ....... 382 

Vocal cords . . .197, 393 

sounds, varieties of ... . 394 

Voice, production of ..... . 393 

W. 

Water 20 

elimination of by kidney . 244 

functions of in body . . 20 

Wharton's duct 56 



442 



INDEX. 



White corpuscles 183 

chemical composition of 185 
classes of . . .184 

functions of . . . .184 
origin of . . . 185 

properties of 183 

Wirsung, duct of ... . .66 

Wolffian bodies . . ... 430 

Wrisberg, nerve of . . . 355 



X. 

Xanthin, discharge of 248 

Y. 
Yawning 209 

Z. 

Zymogen 67 



A Classified Catalogue of 
Books on Medicine and the 
Collateral Sciences, Phar- 
macy, Dentistry, Chemistry, 
Hygiene, Microscopy, Etc. 



d£ 



P. Blakiston's Son & Company, Pub- 
lishers of Medical and Scientific Books, 
1012 Walnut Street, Philadelphia 

No. 8. 10-4-01. 



SUBJECT INDEX. 



Special Catalogues of Books on Pharmacy, Dentistry, 
Chemistry, Hygiene, and Nursing will be sent free upon 
application. All inquiries regarding prices, dates of edition, 
terms, etc., will receive prompt attention. 



SUBJECT PAGE 

Alimentary Canal (see Surgery) 19 

Anatomy 3 

Anesthetics 14 

Autopsies (see Pathology) 16 

Bacteriology (see Pathology).. 16 

Bandaging (see Surgery) 19 

Blood, Examination of 16 

Brain 4 

Chemistry. Physics 4 

Children, Diseases of 6 

Climatology 14 

Clinical Charts 20 

Compends 22, 23 

Consumption (see Lungs) 11 

Cyclopedia of Medicine 8 

Dentistry 7 

Diabetes (see Urin. Organs).. 21 

Diagnosis 6 

Diagrams (see Anatomy) 3 

Dictionaries, Cyclopedias 8 

Diet and Food 14 

Dissectors 3 

Ear 9 

Electricity 9 

Embryology 3 

Emergencies , 19 

Eye 9 

Fevers ., 9 

Food 14 

Gout 10 

Gynecology 21 

Hay Fever 20 

Heart 10 

Histology 10 

Hydrotherapy 14 

Hygiene 11 

Hypnotism 14 

Insanity 4 

Intestines (see Miscellaneous) 14 
Latin, Medical (see Miscella- 
neous and Pharmacy) 14, 16 

Life Insurance 14 

Lungs 11 

Massage 12 

Materia Medica 12 

Mechanotherapy 12 

Medical Jurisprudence 13 



SUBJECT. PAGE 

Mental Therapeutics 4 

Microscopy 13 

Milk Analysis (see Chemistry) 4 

Miscellaneous 14 

Nervous Diseases 14 

Nose 20 

Nursing 15 

Obstetrics 16 

Ophthalmology 9 

Organotherapy 14 

Osteology (see Anatomy) 3 

Pathology 16 

Pharmacy 16 

Physical Diagnosis 6 

Physical Training 12 

Physiology 17 

Pneumotherapy 14 

Poisons (see Toxicology) 13 

Practice of Medicine 18 

Prescription Books 18 

Refraction (see Eye) 9 

Rest 14 

Rheumatism 10 

Sanitary Science 11 

Skin 19 

Spectacles (see Eye) 9 

Spine (see Nervous Diseases) 14 
Stomach (see Miscellaneous)... 14 

Students' Compends 22, 23 

Surgery and Surgical Dis- 
eases 19 

Technological Books 4 

Temperature Charts 6 

Therapeutics 12 

Throat 20 

Toxicology 13 

Tumors (see Surgery) 19 

U. S. Pharmacopoeia 17 

Urinary Organs 20 

Urine 20 

Venereal Diseases 21 

Veterinary Medicine 21 

Visiting Lists, Physicians'. 
{Send for Special Circular.) 

Water Analysis 11 

Women, Diseases of. 21 



Self-Examination for Medical Students. . 3500 Questions on 
Medical Subjects, with References to standard Works in which the 
correct replies will be found Together with Questions from State 
Examining Boards. 3d Edition. Just Ready. Paper Cover, 10 cts. 



SUBJECT CATALOGUE OF MEDICAL BOOKS. 3 

SPECIAL NOTM.— The prices given in this catalogue are 
net, no discount can be allowed retail purchasers under any considera- 
tion. This rule has been established in order that everyone will be 
treated alike, a general reduction in former prices having been made to 
meet previous retail discounts. Upon receipt of the advertised price any 
book will be forwarded by mail or express, all charges prepaid. 



ANATOMY. 

MORRIS. Text-Book of Anatomy. 2d Edition. Revised and 
Enlarged. 790 Illustrations, 214 of which are printed in colors. 
Thumb Index in Each CoJ>y. Cloth, $6.00 ; Leather, $7.00 

•' The ever-growing popularity of the book with teachers and students 

is an index of its value." — Medical Record, New York. 

BROOMELL. Anatomy and Histology of the Human Mouth 
and Teeth. 284 Illustrations. #450 

CAMPBELL. Dissection Outlines. Based on Morris' Anatomy. 
2d Edition. .50 

DEAVER. Surgical Anatomy. A Treatise on Anatomy in its 
Application to Medicine and Surgery. With 400 very Handsome full- 
page Illustrations Engraved from Original Drawings made by special 
Artists from dissections prepared for the purpose. Three Volumes. 
Cloth, #2100; Half Morocco or Sheep, $24.00; Half Russia, $27.00 

GORDINIER. Anatomy of the Central Nervous System. 
With 271 Illustrations, many of which are original. Cloth, $6.00 

HEATH. Practical Anatomy. 8th Edition. 300 Illus. $4.25 

HOLDEN. Anatomy. A Manual of Dissections. Revised by A. 
Hkwson, m.d., Demonstrator of Anatomy, Jefferson Medical College, 
Philadelphia. 320 handsome Illustrations. 7th Edition. In two 
compact i2mo Volumes. 850 Pages. Large New Type. Just Ready. 
Vol. I. Scalp— Face— Orbit— Neck— Throat— Thorax— Upper Ex- 
tremity. $1.50 
Vol. II. Abdomen — Perineum — Lower Extremity — Brain — Eye — 
Ear— Mammary Gland — Scrotum — Testes. $1.50 

HOLDEN. Human Osteology. Comprising a Description of the 
Bones, with Colored Delineations of the Attachments of the Muscles. 
The General and Microscopical Structure of Bone and its Develop- 
ment. With Lithographic Plates and numerous Illus. 8th Ed. $5.25 

HOLDEN. Landmarks. Medical and Surgical. 4th Ed. .75 

HUGHES AND KEITH. Dissections. In three Parts: I, Upper 
and Lower Extremity ; II, Abdomen, Pelvis ; II I, Perineum, 
Thorax. With Colored and other Illustrations. In Press. 

MACALISTER. Human Anatomy. Systematic and Topograph- 
ical. 816 Illustrations. Cloth, $5.00; Leather, $6.00 

McMURRICH. Embryology. Illustrated. In Press. 

MARSHALL. Physiological Diagrams. Life Size. Colored. 
Eleven Life-Size Diagrams (each seven feet by three feet seven 
inches). Designed for Demonstration before the Class. 

In Sheets, Unmounted, $40.00 ; Backed with Muslin and Mounted 
on Rollers, $60.00; Ditto, Spring Rollers, in Handsome Walnut Wall 
Map Case, $100.00; Single Plates — Sheets, $5.00 ; Mounted, $7.50. 
Explanatory Key, .50. Purchaser must pay freight charges. 

POTTER. Compend of Anatomy, Including Visceral Anatomy. 
6th Ed. 16 Lith. Plates and 117 other Illus. .80 ; Interleaved, $1.00 

WILSON. Anatomy, nth Edition. 429 Illus., 26 Plates. $5.00 

WINDLE. Surface Anatomy. Colored and other Illus. $1.00 



SUBJECT CATALOGUE. 



BRAIN AND INSANITY (see also 
Nervous Diseases). 

BLACKBURN. A Manual of Autopsies. Designed for the Use 
of Hospitals for the Insane and other Public Institutions. Ten full- 
page Plates and other Illustrations. $*•*$ 

DERCUM. Mental Therapeutics, Rest, etc. Nearly Ready. 

GORDINIER. The Gross and Minute Anatomy of the Central 
Nervous System. With full-page and other Illustrations. $6.00 

HORSLEY. The Brain and Spinal Cord. The Structure and 
Functions of. Numerous Illustrations. $2.50 

IRELAND. The Mental Affections of Children. 2d Ed. $4.00 

LEWIS (BEVAN). Mental Diseases. A Text-Book Having 
Special Reference to the Pathological Aspects of Insanity. 26 Litho- 
graphic Plates and other Illustrations. 2d Ed. $7.00 

MANN. Manual of Psychological Medicine and Allied 
Nervous Diseases, $3.00 

PERSHING. Diagnosis of Nervous and Mental Disease. 
Illustrated. Just Ready. $1.25 

REGIS. Mental Medicine. Authorized Translation by H. M. 
Bannister, m.d. $2.00 

SHUTTLE WORTH. Mentally Deficient Children. $1.50 

STEARNS. Mental Diseases. With a Digest of Laws Relating 
to Care of Insane. Illustrated. Cloth, $2.75 ; Sheep, #3.25 

TUKE. Dictionary of Psychological Medicine. Giving the 
Definition, Etymology, and Symptoms of the Terms used in Medical 
Psychology, with the Symptoms, Pathology, and Treatment of the 
Recognized Forms of Mental Disorders. Two volumes. $10.00 

WOOD, H. C. Brain and Overwork. .40 



CHEMISTRY AND TECHNOLOGY. 

Special Catalogue of Chemical Books sent free upon application. 

ALLEN. Commercial Organic Analysis. A Treatise on the 

Modes of Assaying the Various Organic Chemicals and Products 

Employed in the Arts, Manufactures, Medicine, etc., with concise 

methods for the Detection of Impurities, Adulterations, etc. 8vo. 

Vol. I. Alcohols, Neutral Alcoholic Derivatives, etc., Ethers, Veg- 
etable Acids, Starch, Sugars, etc. 3d Edition. #4-5° 

Vol. II, Part I. Fixed Oils and Fats, Glycerol, Explosives, etc. 
3d Edition. $3-5° 

Vol. II, Part II. Hydrocarbons, Mineral Oils, Lubricants, Benzenes, 
Naphthalenes and Derivatives, Creosote, Phenols, etc. 3d Ed. ^3.50 

Vol. II, Part HI. Terpenes, Essential Oils, Resins, Camphors, etc. 
3d Edition. Preparing. 

Vol. HI, Part I. Tannins, Dyes and Coloring Matters. 3d Edition. 
Enlarged and Rewritten. Illustrated. $4^5° 

Vol. Ill, Part II. The Amines, Hydrazines and Derivatives, 
Pyridine Bases. The Antipyretics, etc. Vegetable Alkaloids, Tea, 
Coffee, Cocoa, etc. 8vo. 2d Edition. #4-5° 

Vol. Ill, Part III. Vegetable Alkaloids, Non-Basic Vegetable Bitter 
Principles. Animal Bases, Animal Acids, Cyanogen Compounds, 
etc. 2d Edition, 8vo. $4-5° 

Vol. IV. The Proteids and Albuminous Principles. 2d Ed. $4. 50 



MEDICAL BOOKS. 



BAILEY AND CADY. Chemical Analysis. Just Ready. $1.25 

BARTLEY. Medical and Pharmaceutical Chemistry. A 
Text-Book for Medical, Dental, and Pharmaceutical Students. With 
Illustrations, Glossary, and Complete Index. 5th Edition. ' $3.00 

BARTLEY. Clinical Chemistry. The Examination of Feces, 
Saliva, Gastric Juice, Milk, and Urine. $1.00 

BLOXAM. Chemistry, Inorganic and Organic. With Experi- 
ments. 9th Ed., Revised. 281 Engravings. Preparing. 

CALDWELL. Elements of Qualitative and Quantitative 
Chemical Analysis. 3d Edition, Revised. $1.00 

CAMERON. Oils and Varnishes. With Illustrations. $2.25 

CAMERON. Soap and Candles. 54 Illustrations #2.00 

CLOWES AND COLEMAN. Quantitative Analysis. 5th 
Edition. 122 Illustrations. $3-5° 

COBLENTZ. Volumetric Analysis. Illustrated Just Ready. #1.25 

CONGDON. Laboratory Instructions in Chemistry. With 
Numerous Tables and 56 Illustrations. Just Ready. $1.00 

GARDNER. The Brewer, Distiller, and Wine Manufac- 
turer. Illustrated. $1.50 

GRAY. Physics. Volume I. Dynamics and Properties of Matter. 
350 Illustrations. Just Ready. $4-5o 

GROVES AND THORP. Chemical Technology. The Appli- 
cation of Chemistry to the Arts and Manufactures. 
Vol. I. Fuel and Its Applications. 607 Illustrations and 4 Plates. 

Cloth, $5.00; Yz M or., $6.50 
Vol.11. Lighting. Illustrated. Cloth, #4.00; %Mor.,$5.5o 

Vol. III. Gas Lighting. Cloth, $3.50; ^ Mor., $4.50 

Vol. IV. Electric Lighting. Photometry. In Press. 

HOLLAND. The Urine, the Gastric Contents, the Common 
Poisons, and the Milk. Memoranda, Chemical and Microscopi- 
cal, for Laboratory Use. 6th Ed. Illustrated and interleaved, $1.00 

LEFFMANN. Compend of Medical Chemistry, Inorganic 
and Organic. 4th Edition, Revised. .80; Interleaved, $1. 00 

LEFFMANN. Analysis of Milk and Milk Products. 2d 
Edition, Enlarged. Illustrated. $1.25 

LEFFMANN. Water Analysis. For Sanitary and Technic Pur- 
poses. Illustrated. 4th Edition. #1-25 

LEFFMANN. Structural Formulae. Including 180 Structural 
and Stereo-Chemical Formulae. i2mo. Interleaved. $1.00 

LEFFMANN AND BEAM. Select Methods in Food Analy- 
sis. Illustrated Just Ready. $2.50 

MUTER. Practical and Analytical Chemistry. 2d American 
from the Eighth English Edition. Revised to meet the requirements 
of American Students. 56 Illustrations. $1.25 

OETTEL. Exercises in Electro-Chemistry. Illustrated. .75 

OETTEL. Electro-Chemical Experiments. Illustrated. .75 

RICHTER. Inorganic Chemistry. 5th American from 10th Ger- 
man Edition. Authorized translation by Edgar F. Smith, m.a., 
ph.d. 89 Illustrations and a Colored Plate. $i-75 

RICHTER. Organic Chemistry. 3d American Edition. Trans, 
from the 8th German by Edgar F. Smith. Illustrated. 2 Volumes. 
Vol. I. Aliphatic Series. 625 Pages. $3.00 

Vol. II. Carbocvclic Series. 671 Pages. $3.00 

ROCKWOOD. Chemical Analysis for Students of Medicine, 
Dentistry, and Pharmacy. Illustrated. Just Ready. 

SMITH. Electro-Chemical Analysis. 2d Ed. 28 Illus. $1.25 

SMITH AND KELLER. Experiments. Arranged for Students 
in General Chemistry. 4th Edition. Illustrated. .60 



SUBJECT CATALOGUE. 



SUTTON. Volumetric Analysis. A Systematic Handbook for 
the Quantitative Estimation of Chemical Substances by Measure, 
Applied to Liquids, Solids, and Gases. 8th Edition, Revised. 112 
Illustrations. $5.00 

SYMONDS. Manual of Chemistry, for Medical Students. 

2d Edition. $2.00 

TRAUBE. Physico-Chemical Methods. Translated by Hardin. 

97 Illustrations. #1.50 

THRESH. Water and Water Supplies. 3d Edition. $2.00 

ULZER AND FRAENKEL. Chemical Technical Analysis. 

Translated by Fleck. Illustrated. $1.25 

WOODY. Essentials of Chemistry and Urinalysis. 4th 

Edition. Illustrated. $1.50 

*** Special Catalogue of Books on Chemistry free upon application. 

CHILDREN. 

CAUTLEY. Feeding of Infants and Young Children by Nat- 
ural and Artificial Methods. $2.00 
HALE. On the Management of Children. .50 

HATFIELD. Compend of Diseases of Children. With a 
Colored Plate. 2d Edition. .80; Interleaved, $1.00 

IRELAND. The Mental Affections of Children. 2d Ed. #4.00 

MEIGS. Infant Feeding and Milk Analysis. The Examination 
of Human and Cow's Milk, Cream, Condensed Milk, etc., and 
Directions as to the Diet of Young Infants. .50 

POWER. Surgical Diseases of Children and their Treat- 
ment by Modern Methods. Illustrated. $2.50 

SHUTTLEWORTH. Mentally Deficient Children. New 
Edition. $1.50 

STARR. The Digestive Organs in Childhood. The Diseases of 
the Digestive Organs in Infancy and Childhood. 3d Edition, Rewrit- 
ten and Enlarged. Illustrated. Just Ready. $3.00 

STARR. Hygiene of the Nursery. Including the General Regi- 
men and Feeding of Infants and Children, and the Domestic Manage- 
ment of the Ordinary Emergencies of Early Life, Massage, etc. 6th 
Edition. 25 Illustrations. #1.00 

SMITH. Wasting Diseases of Children. 6th Edition. #2.00 

TAYLOR AND WELLS. The Diseases of Children. 2d Edi- 
tion, Revised and Enlarged. Illustrated. 8vo. Just Ready. $4.50 

DIAGNOSIS. 

BROWN. Medical Diagnosis. A Manual of Clinical Methods. 

4th Edition. 112 Illustrations. Cloth, $2.25 

DA COSTA. Clinical Examination of the Blood. Illustrated. 

In Press. 
EMERY. Bacteriological Diagnosis. In Press. 

MEMMINGER. Diagnosis by the Urine. 2d Ed. 24 Illus. $1.00 






MEDICAL BOOKS. 



PERSHING. Diagnosis of Nervous and Mental Diseases. 
Illustrated. Just Ready. $ J -25 

STEELL. Physical Signs of Pulmonary Disease. #1.25 

TYSON. Hand-Book of Physical Diagnosis. For Students and 
Physicians. By the Professor of Clinical Medicine in the University 
of Pennsylvania. Illus. 4th Ed.. Improved and Enlarged. With 
Two Colored and 55 other Illustrations. Just Ready. $1.50 



DENTISTRY. 

Special Catalogue of Dental Books sent free upon application. 

BARRETT. Dental Surgery for General Practitioners and 
Students of Medicine and Dentistry. Extraction of Teeth, 
etc. 3d Edition. Illustrated. $1.00 

BROOMELL. Anatomy and Histology of the Human Mouth 
and Teeth. 284 Handsome Illustrations. $4-5o 

FILLEBROWN. A Text-Book of Operative Dentistry. 

Written by invitation of the National Association of Dental Facul- 
ties. Illustrated. $2.25 

GORGAS. Dental Medicine. A Manual of Materia Medica and 
Therapeutics. 7th Edition. Just Ready. Cloth, $4.00; Sheep, #5.00 

GORGAS. Questions and Answers for the Dental Student. 
Embracing all the subjects in the Curriculum of the Dental Student. 
Octavo. Just Ready. $6.00 

HARRIS. Principles and Practice of Dentistry. Including 
Anatomy, Physiology, Pathology, Therapeutics, Dental Surgery, 
and Mechanism. 13th Edition. Revised by F. J. S. Gorgas, m.d., 
d.d.s. 1250 Illustrations. Cloth, $6.00; Leather, #7.00 

HARRIS. Dictionary of Dentistry. Including Definitions of Such 
Words and Phrases of the Collateral Sciences as Pertain to the Art and 
Practice of Dentistry. 6th Edition. Revised and Enlarged by Fer- 
dinand F. S. Gorgas, m.d., d.d.s. Cloth, $5.00 ; Leather, $6.00 

HEATH. Injuries and Diseases of the Jaws. 4th Edition. 187 
Illustrations. #4.50 

RICHARDSON. Mechanical Dentistry. 7th Edition. Thor- 
oughly Revised and Enlarged by Dr. Geo. W. Warren. 691 Illus- 
trations. Cloth, $5.00; Leather, #6.00 

SMITH. Dental Metallurgy. Illustrated. $1.75 

TAFT. Index of Dental Periodical Literature. #2.00 

TOMES. Dental Anatomy. Human and Comparative. 263 Illus- 
trations. 5th Edition. £4.00 
TOMES. Dental Surgery. 4th Edition. 289 Illustrations. #4.00 

WARREN. Compend of Dental Pathology and Dental Medi- 
cine. With a Chapter on Emergencies. 3d Edition. Illustrated. 

.80; Interleaved, #1.25 

WARREN. Dental Prosthesis and Metallurgy. 129 Ills. $1.25 
WHITE. The Mouth and Teeth. Illustrated. .40 



SUBJECT CATALOGUE. 



DICTIONARIES. 

GOULD. The Illustrated Dictionary of Medicine, Biology, 
and Allied Sciences. Being an Exhaustive Lexicon of Medicine 
and those Sciences Collateral to it: Biology (Zoology and Botany), 
Chemistry, Dentistry, Parmacology, Microscopy, etc., with many 
useful Tables and numerous fine Illustrations. 1633 pages. 5th Ed. 
Sheep or Half Dark Green Leather, $10.00; Thumb Index, $11.00 
Half Russia, Thumb Index, $12.00 

GOULD. The Medical Student's Dictionary, nth Edition. 
Illustrated. Including all the Words and Phrases Generally Used 
inMedicine, with their Proper Pronunciation and Definition, Based 
on Recent Medical Literature. With a new Table of Eponymic 
Terms and Tests and Tables of the Bacilli, Micrococci, Mineral 
Springs, etc., of the Arteries, Muscles, Nerves, Ganglia, Plexuses, etc. 
nth Edition. Enlarged by over 100 pages and illustrated with a 
large number of engravings. 840 pages. 

Half Green Morocco, $2.50; Thumb Index, $3.00 

GOULD. The Pocket Pronouncing Medical Lexicon. 4th Edi- 
tion. (30,000 Medical Words Pronounced and Defined.) Containing 
all the Words, their Definition and Pronunciation, that the Medical, 
Dental, or Pharmaceutical Student Generally Comes in Contact 
With ; also Elaborate Tables of Eponymic Terms, Arteries, Muscles, 
Nerves, Bacilli, etc., etc., a Dose List in both English and Metric 
Systems, etc., Arranged in a Most Convenient Form for Reference and 
Memorizing. A new (Fourth) Edition, Revised and Enlarged. 
838 pages. 

Full Limp Leather, Gilt Edges, $1.00 ; Thumb Index, $1.25 
120,000 Copies of Gould's Dictionaries Have Been Sold. 

GOULD AND PYLE. Cyclopedia of Practical Medicine and 
Surgery. Seventy-two Special Contributors. Illustrated. 
One Volume. A Concise Reference Handbook, Alphabetically 
Arranged, of Medicine, Surgery, Obstetrics, Materia Medica, 
Therapeutics, and the Various Specialties, with Particular Reference 
to Diagnosis and Treatment. Compiled under the Editorial Super- 
vision of George M. Gould, m.d., Author of "An Illustrated 
Dictionary of Medicine " • Editor " Philadelphia Medical Journal/' 
etc.; and Walter L. Pyle, m.d., Assistant Surgeon Wills Eye 
Hospital ; formerly Editor " International Medical Magazine," etc., 
and Seventy-two Special Contributors. With many Illustrations. 
Large Square 8vo, to correspond with Gould's "Illustrated Dic- 
tionary." Just Ready. Full Sheep or Half Dark-Green Leather, $10.00 
With Thumb Index, $11.00; Ha f Russia, Thumb Index, $12.00 net. 
*sj,* Sample Pages and Illustrations and Descriptive Circulars of 

Gould's Dictionaries and Cyclopedia sent free upon application. 

HARRIS. Dictionary of Dentistry. Including Definitions of Such 
Words and Phrases of the Collateral Sciences as Pertain to the Art 
and Practice of Dentistry. 6th Edition. Revised and Enlarged by 
Ferdinand J. S. Gorgas, m.d., d.d.s. Cloth, $5.00; Leather, $6 00 

LONGLEY. Pocket Medical Dictionary. With an Appendix, 
containing Poisons and their Antidotes, Abbreviations used in Pre- 
scriptions, etc. Cloth, .75 ; Tucks and Pocket, $1.00 

MAXWELL, Terminologia Medica Polyglotta. By Dr. 
Theodore Maxwell, Assisted by Others. $3.00 

The object of this work is to assist the medical men ot any nationality 

in reading medical literature written in a language not their own. 

Each term is usually given in seven languages, viz. : English, French, 

German, Italian, Spanish, Russian, and Latin. 

TREVES AND LANG. German-English Medical Dictionary . 

Half Russia, $3.25 



MEDICAL BOOKS. 



EAR (see also Throat and Nose). 

BURNETT. Hearing and How to Keep It. Illustrated. .40 

DALBY. Diseases and Injuries of the Ear. 4th Edition. 38 
Wood Engravings and 8 Colored Plates. #2.50 

HOVELL. Diseases of the Ear and Naso-Pharynx. Includ- 
ing Anatomy and Physiology of the Organ, together with the Treat- 
ment of the Affections of the Nose and Pharynx which Conduce to 
Aural Disease. 128 Illustrations. 2d Edition. Just Ready. $5.50 

PRITCHARD. Diseases of the Ear. 3d Edition, Enlarged. 
Many Illustrations and Formulae. $1.50 



ELECTRICITY. 

BIGELOW. Plain Talks on Medical Electricity and Bat- 
teries. With a Therapeutic Index and a Glossary. 43 Illustra- 
tions. 2d Edition. #1.00 

HEDLEY. Therapeutic Electricity and Practical Muscle 
Testing. 99 Illustrations. #2.50 

JACOBY. Electrotherapy. 2 Volumes. Illustrated. Including 
Special Articles by Special Authors. Just Ready. 

JONES. Medical Electricity. 3d Edition. 117 Illus. $3.00 



EYE. 

A Special Circular of Books on the Eye sent free upon application . 

DONDERS. The Nature and Consequences of Anomalies of 
Refraction. With Portrait and Illustrations. Half Morocco, $1.25 

FICK. Diseases of the Eye and Ophthalmoscopy. Trans- 
lated by A. B. Hale, m. d. 157 Illustrations, many of which are in 
colors, and a glossary. Cloth, $4.50; Sheep, $5.50 

GOULD AND PYLE. Compend of Diseases of the Eye and 
Refraction. Including Treatment and Operations, and a Section 
on Local Therapeutics. With Formulae, Useful Tables, a Glossary, 
and in Illus., several of which are in colors. 2d Edition, Revised. 

Cloth, .80; Interleaved, $1.00 

HARLAN. Eyesight, and How to Care for It. Illus. .40 

HARTRIDGE. Refraction. 104 Illustrations and Test Types. 
nth Edition, Enlarged fust Ready. #1.50 

HARTRIDGE. On the Ophthalmoscope. 4th Edition. With 
4 Colored Plates and 68 Wood-cuts. Just Ready. #1.50 

HANSELL AND REBER. Muscular Anomalies of the Eye. 

Illustrated. $1.50 

HANSELL AND BELL. Clinical Ophthalmology. Colored 
Plate of Normal Fundus and 120 Illustrations. #1.50 



10 SUBJECT CATALOGUE. 

MORTON. Refraction of the Eye. Its Diagnosis and the Cor- 
rection of its Errors. 6th Edition. $1.00 

OHLEMANN. Ocular Therapeutics. Authorized Translation, 
and Edited by Dr. Charles A. Oliver. £*-75 

PHILLIPS. Spectacles and Eyeglasses. Their Prescription 
and Adjustment. 2d Edition. 49 Illustrations. #1.00 

SWANZY. Diseases of the Eye and Their Treatment. 7th 

Edition, Revised and Enlarged. 164 Illustrations, 1 Plain Plate, 
and a Zephyr Test Card. $2.50 

THORINGTON. Retinoscopy. 4th Edition. Carefully Revised. 
Illustrated. Just Ready. $1.00 

THORINGTON. Refraction and How to Refract, soo Illustra- 
tions, 13 of which are Colored. 2d Edition. $1.50 

WALKER. Students' Aid in Ophthalmology. Colored Plate 
and 40 other Illustrations and Glossary. $1.50 

WRIGHT. Ophthalmology. 2d Edition, Revised and Enlarged. 
117 Illustrations and a Glossary. Just Ready. $3.00 

FEVERS. 

GOODALL AND WASHBOURN. Fevers and Their Treat- 
ment. Illustrated. $3.00 

GOUT AND RHEUMATISM. 

DUCKWORTH. A Treatise on Gout. With Chromo-lithographs 
and Engravings. Cloth, $6.00 

HAIG. Causation of Disease by Uric Acid. A Contribution to 
the Pathology of High Arterial Tension, Headache, Epilepsy, Gout, 
Rheumatism, Diabetes, etc. 5th Edition. $3. 00 

HEART. 

THORNE. The Schott Methods of the Treatment of Chronic 
Heart Disease. Third Edition. Illustrated. $ 1 -7S 

HISTOLOGY. 

CUSHING. Compend of Histology. By H. H. Cushing, m.d.. 
Demonstrator of Histology, Jefferson Medical College, Philadelphia. 
Illustrated. Nearly Re aay. .80; Interleaved, $1. 00 

STIRLING. Outlines of Practical Histology. 368 Illustrations. 
2d Edition, Revised and Enlarged. With new Illustrations. $2.00 

STOHR. Histology and Microscopical Anatomy. Edited by 
A. Schaper, m.d., University of Breslau, formerly Demonstrator of 
Histology, Harvard Medical School. Fourth American from 9th Ger- 
man Edition, Revised and Enlarged. 379 Ulus. fust Ready. $3.00 



MEDICAL BOOKS. 



HYGIENE AND WATER ANALYSIS. 

Special Catalogue of Books on Hygiene sent free upon application . 

CANFIELD. Hygiene of the Sick-Room. A Book for Nurses 
and Others. Being a Brief Consideration of Asepsis, Antisepsis, Dis- 
infection, Bacteriology, Immunity, Heating, Ventilation, etc. #1.25 

CONN. Agricultural Bacteriology. Illus. Just Ready. #2.50 

COPLIN. Practical Hygiene. A Complete American Text-Book. 
138 Illustrations. New Edition. Preparing. 

HARTSHORNE. Our Homes. Illustrated. .40 

KENWOOD. Public Health Laboratory Work. 116 Illustra- 
tions and 3 Plates. $2.00 

LEFFMANN. Select Methods in Food Analysis. 53 Illustra- 
tions and 4 Plates. Just Ready. $2.50 

LEFFMANN. Examination of "Water for Sanitary and 
Technical Purposes. 4th Edition. Illustrated. $1.25 

LEFFMANN. Analysis of Milk and Milk Products. Illus- 
trated. Second Edition. $1.25 

LINCOLN. School and Industrial Hygiene. .40 

McFARLAND. Prophylaxis and Personal Hygiene. In Press. 

NOTTER. The Theory and Practice of Hygiene. 15 Plates 
and 138 other Illustrations. 8vo. 2d Edition. $7.00 

PARKES. Hygiene and Public Health. By Louis C. Parkes, 
m.d. 6th Edition. Enlarged. Illustrated. Just Ready. #3.00 

PARKES. Popular Hygiene. The Elements of Health. A Book 
for Lay Readers. Illustrated. #1.25 

STARR. The Hygiene of the Nursery. Including the General 
Regimen and Feeding of Infants and Children, and the Domestic 
Management of the Ordinary Emergencies of Early Life, Massage, 
etc. 6th Edition. 25 Illustrations. #1.00 

STEVENSON AND MURPHY. A Treatise on Hygiene. By 
Various Authors. In Three Octave Volumes. Illustrated. 

Vol. I, $6.00; Vol. II, £6.00; Vol. Ill, $5.00 
*** Each Volume sold separately. Special Circular upon application. 

THRESH. Water and Water Supplies. 3d Edition. $2.00 

WILSON. Hand-Book of Hygiene and Sanitary Science. 

Wiih Illustrations. 8th Edition. $3-oo 

WEYL. Sanitary Relations of the Coal-Tar Colors. Author- 
ized Translation by Henry Leffmann, m.d., ph.d. $1.25 



LUNGS AND PLEURA. 

KNOPF. Pulmonary Tuberculosis. Its Modern Prophylaxis 
and Treatment in Special Institutions and at Home. Illus. #3.00 

STEELL. Physical Signs of Pulmonary Disease. Illus. #1.25 



12 SUBJECT CATALOGUE. 

MASSAGE— PHYSICAL EXERCISE. 

OSTROM. Massage and the Original Swedish Move- 
ments. Their Application to Various Diseases of the Body. A 
Manual for Students, Nurses, and Physicians. Fourth Edition, En- 
larged. 105 Illustrations, many of which are original. $1.00 

MITCHELL AND GULICK. Mechanotherapy. Illus. InPress. 
TREVES. Physical Education. Methods, etc. .75 

WARD. Notes on Massage. Interleaved. Paper cover, $1. 00 



MATERIA MEDICA AND THERA- 
PEUTICS. 

BIDDLE. Materia Medica and Therapeutics. Including Dose 
List, Dietary for the Sick, Table of Parasites, and Memoranda ot 
New Remedies. 13th Edition, Revised. 64 Illustrations and a 
Clinical Index. Cloth, $4.00; Sheep, $5.00 

BRACKEN. Outlines of Materia Medica and Pharmacology. #2.75 

COBLENTZ. The Newer Remedies. Including their Synonyms, 
Sources, Methods of Preparation, Tests, Solubilities, Doses, etc. 
3d Edition, Enlarged and Revised. #1.00 

COHEN. Physiologic Therapeutics. Mechanotherapy, Mental 
Theiapeutics, Electrotherapy. Climatology, Hydrotherapy, Pneu- 
matotheiapy, Prophylaxis, Dietetics, etc. n Volumes. Octavo. 
Illustrated. 5 Volumes now ready. 

Special Descriptive Circular will be sent upon applicatio7i. 
DAVIS. Materia Medica and Prescription Writing. $1.50 

GORGAS. Dental Medicine. A Manual of Materia Medica and 
Therapeutics. 7th Edition, Revised, fust Ready. $4.00 

GROFF. Materia Medica for Nurses, with questions for Self Exam- 
ination and a complete Glossary. #1.25 

HELLER. Essentials of Materia Medica, Pharmacy, and 
Prescription Writing. $1.50 

MAYS. Theine in the Treatment of Neuralgia. % bound, .50 

POTTER. Hand-Book of Materia Medica, Pharmacy, and 
Therapeutics, including the Action of Medicines, Special Therapeu- 
tics, Pharmacology, etc., including over 600 Prescriptions and For- 
mulae. 8th Edition, Revised and Enlarged. With Thumb Index in 
each copy. Just Ready. Cloth, $5.00; Sheep, $6.00 

POTTER. Compend of Materia Medica, Therapeutics, and 

Prescription Writing, with Special Reference to the Physiologi- 
cal Action of Drugs. 6th Edition. .80; Interleaved, $1. 00 

MURRAY. Rough Notes on Remedies. 4th Edition. £1.25 



MEDICAL BOOKS. 13 



SAYRE. Organic Materia Medica and Pharmacognosy. An 

Introduction to the Study of the Vegetable Kingdom and the Vege- 
table and Animal Drugs. Comprising the Botanical and Physical 
Characteristics, Source, Constituents, and Pharmacopeial Prepara- 
tions, Insects Injurious to Drugs, and Pharmacal Botany. With 
sections on Histology and Microtechnique, by W. C. Stevens. 
374 Illustrations, many of which are original. 2d Edition. 

Cloth, $4.50 

TAVERA. Medicinal Plants of the Philippines. Just Ready. 

$2.00 

WHITE AND WILCOX. Materia Medica, Pharmacy, Phar- 
macology, and Therapeutics. 5th American Edition, Revised by 
Reynold W. Wilcox, m.a., m.d., ll.d., Professor of Clinical 
Medicine and Therapeutics at the New York Fost-Graduate Medical 
School. Just Ready. Cloth, $3.00; Leather, $3.50 

" The care with which Dr. Wilcox has performed his work is con- 
spicuous on every page, and it is evident that no recent drug possess- 
ing any merit has escaped his eye. We believe, on the whole, this is 
the best book on Materia Medica and Therapeutics to place in the 
hands of students, and the practitioner will find it a most satisfactory 
work for daily use." — The Cleveland Medical Gazette. 



MEDICAL JURISPRUDENCE AND 
TOXICOLOGY. 

REESE. Medical Jurisprudence and Toxicology. A Text-Book 
for Medical and Legal Practitioners and Students. 5th Edition. 
Revised by Henry Leffmann, m.d. Clo.,$3.oo; Leather, $3.50 

" To the student of medical jurisprudence and toxicology it is in- 
valuable, as it is concise, clear, and thorough in every respect." — The 
American Journal of the Medical Sciences. 

MANN. Forensic Medicine and Toxicology. Illus. $6.50 

TANNER. Memoranda of Poisons. Their Antidotes and Tests. 
8th Edition, by Dr Henry Leffmann. Just Ready. .75 



MICROSCOPY. 

CARPENTER. The Microscope and Its Revelations. 8th 

Edition, Revised and Enlarged 817 Illustrations and 23 Plates. 
Just Ready. Cloth, #8.co ; Half Morocco, $9.00 

LEE. The Microtomist's Vade Mecum. A Hand-Book of 
Methods of Microscopical Anatomy. 887 Articles. 5th Edition, 
Enlarged. #4.00 

REEVES. Medical Microscopy, including Chapters on Bacteri- 
ology* Neoplasms, Urinary Examination, etc. Numerous Illus- 
trations, some of which are printed in colors. $2.50 

WETHERED. Medical Microscopy. A Guide to the Use of the 
Microscope in Practical Medicine. 100 Illustrations. $2.00 



14 SUBJECT CATALOGUE. 

MISCELLANEOUS. 

BERRY. Diseases of Thyroid Gland. Illustrated. $4.00 

BURNETT. Foods and Dietaries. A Manual of Clinical Diet- 
etics. 2d Edition. |i-5o 
BUXTON. Anesthetics. Illustrated. 3d Edition. $1.50 
COHEN. Organotherapy. In Press. 
DAVIS. Dietotherapy. Food in Health and Disease. In Press. 
GOULD. Borderland Studies. Miscellaneous Addresses and 
Essays. i2mo. $2.00 
GREENE. Medical Examination for Life Insurance. Illus- 
trated. $4.00 
HAIG. Causation of Disease by Uric Acid. The Pathology of 
High Arterial Tension, Headache, Epilepsy, Gout, Rheumatism, 
Diabetes, Bright's Disease, etc. sthEdition. $3.00 
HAIG. Diet and Food. Considered in Relation to Strength and 
Power of Endurance. 3d Edition. Just Ready. $1.00 
HEMMETER. Diseases of the Stomach. Their Special Path- 
ology . Diagnosis, and Treatment. With Sections on Anatomy, Diet- 
etics, Surgery, etc. 2d Edition, Revised and Enlarged. Illustrated. 

Cloth", $6.00 ; Sheep, #7.00 
HEMMETER. Diseases of the Intestines. Illustrated. 2 Vol- 
umes. 8vo. Just Ready. #10 00 
HENRY. A Practical Treatise on Anemia. Half Cloth, .50 
LEFFMANN. Food Analysis. Illustrated. Just Ready. $2.50 
NEW SYDENHAM SOCIETY'S PUBLICATIONS. Circulars 
upon application. Per Annum, #8.00 
OSGOOD. The Winter and Its Dangers. .40 
OSLER AND McCRAE. Cancer of the Stomach. $2.00 
PACKARD. Sea Air and Sea Bathing. .40 
RICHARDSON. Long Life and How to Reach It. .40 
ST. CLAIR. Medical Latin. $1.00 
TISSIER. Pneumatotherapy. In Press. 
TURNBULL. Artificial Anesthesia. 4th Edition. Illus. $2.50 
WEBER AND HINSDALE. Climatology. 2 Vols. Illustrated 
with Maps. Just Ready. 
WILSON. The Summer and Its Diseases. .40 
WINTERNITZ. Hydrotherapy. Illustrated. In Press. 



NERVOUS DISEASES. 

DERCUM. Rest, Hypnotism, Mental Therapeutics. In Press. 

GORDINIER. The Gross and Minute Anatomy of the Cen- 
tral Nervous System. With 271 original Colored and other 
Illustrations. Cloth, #6.00; Sheep, #7.00 

GOWERS. Manual of Diseases of the Nervous System. A 
Complete Text-Book. Revised, Enlarged, and in many parts Re- 
written. With many new Illustrations. Two volumes. 
Vol. I. Diseases of the Nerves and Spinal Cord. 3d Edition, En- 
larged. Cloth, $4.00; Sheep, $$. 00 
Vol. II. Diseases of the Brain and Cranial Nerves ; General and 
Functional Disease. 2d Edition. Cloth, $4.00; Sheep, $5.00 

GOWERS. Syphilis and the Nervous System. £1.00 



MEDICAL BOOKS. 15 



GOWERS. Clinical Lectures. A New Volume of Essays on the 
Diagnosis, Treatment, etc., of Diseases of the Nervous System. $2.00 

GOWERS. Epilepsy and Other Chronic Convulsive Diseases. 

2d Edition. Just Ready. $3.00 

HORSLEY. The Brain and Spinal Cord. The Structure and 

Functions of. Numerous Illustrations. $2.50 

ORMEROD. Diseases of the Nervous System. 66 Wood En- 

gravings. $1.00 

OSLER. Chorea and Choreiform Affections. $2.00 

PERSHING. Diagnosis of Nervous and Mental Diseases. 

Illustrated. Just Ready. $*.25 

PRESTON. Hysteria and Certain Allied Conditions. Their 

Nature and Treatment. Illustrated. $2.00 

WOOD. Brain Work and Overwork. .40 

NURSING (see also Massage). 

Special Catalogue of Books for Nurses sent free upon application. 

CANFIELD. Hygiene of the Sick-Room. A Book for Nurses and 
Others. Being a Brief Consideration of Asepsis, Antisepsis, Disinfec- 
tion, Bacteriology, Immunity, Heating and Ventilation, and Kindred 
Subjects for the Use of Nurses and Other Intelligent Women. $1.25 

CUFF. Lectures to Nurses on Medicine. Third Edition. $1.25 

DOMVILLE. Manual for Nurses and Others Engaged in At- 
tending the Sick. 9th Edition. With Recipes for Sick-room Cook- 
ery, etc. In Press, 
FULLERTON. Obstetric Nursing. 41 Ills. 5th Ed. $1.00 
FULLERTON. Surgical Nursing. 3d Ed. 69 Ills. £1.00 

GROFF. Materia Medica for Nurses. With Questions for Self-Ex- 

amination and a very complete Glossary. $1.25 

" It will undoubtedly prove a valuable aid to the nurse in securing a 

knowledge of drugs and their uses/' — The Medical Record. New 

York. 

HUMPHREY. A Manual for Nurses. Including General 

Anatomy and Physiology, Management of the Sick Room, etc. 

23d Edition. 79 Illustrations. $1.00 

" In the fullest sense, Dr. Humphrey's book is a distinct advance on 

all previous manuals. It is, in point of fact, a concise treatise on 

medicine and surgery for the beginner, incorporating with the text the 

management of childbed and the hygiene of the sick-room. Its value 

is greatly enhanced by copious wood -cuts and diagrams of the bones 

and internal organs.*' — British Medical Journal , London. 

STARR. The Hygiene of the Nursery. Including the General 
Regimen and Feeding of Infants and Children, and the Domestic Man- 
agement of the Ordinary Emergencies of Early Life, Massage, etc. 6th 
Edition. 25 Illustrations. #1.00 

TEMPERATURE AND CLINICAL CHARTS. See page 6. 

VOSWINKEL. Surgical Nursing. Second Edition, Enlarged. 
xz2 Illustrations. £1.00 



16 SUBJECT CATALOGUE. 

OBSTETRICS. 

CAZEAUX AND TARNIER. Midwifery. With Appendix by 
Mund6. The Theory and Practice of Obstetrics, including the Dis- 
eases of Pregnancy and Parturition, Obstetrical Operations, etc. 
8th Edition. Illustrated by Colored and other full-page Plates, and 
numerous Wood Engravings. Cloth, $4.50 ; Full Leather, $5.50 

EDGAR. Text-Book of Obstetrics. Illustrated. Preparing. 

FULLERTON. Obstetric Nursing. 5th Ed. Illustrated. $1.00 

LANDIS. Compend of Obstetrics. 7th Edition, Revised by Wm. 
H. Wells, Demonstrator of Clinical Obstetrics, Jefferson Medical 
College. 52 Illustrations. Just Ready. .80; Interleaved, $1.00 

WINCKEL. Text-Book of Obstetrics, Including the Pathol- 
ogy and Therapeutics of the Puerperal State. Authorized 
Translation by J. Clifton Edgar, m.d. Illus. Cloth, $5.00 

PATHOLOGY. 

BARLOW. General Pathology. 795 pages. 8vo. #5.00 

BLACK. Micro-Organisms. The Formation of Poisons. .75 

BLACKBURN. Autopsies. A Manual of Autopsies Designed for 

the Use of Hospitals for the Insane and other Public Institutions. 

Ten full-page Plates and other Illustrations. $1.25 

CONN. Agricultural Bacteriology. Illus. Just Ready. $2.50 
COPLIN. Manual of Pathology. Including Bacteriology, Technic 
of Post-Mortems, Methods of Pathologic Research, etc. 330 Illus- 
trations, 7 Colored Plates. 3d Edition. $3-5o 

DA COSTA. Clinical Pathology of the Blood. Illus. In Press. 
EMERY. Bacteriological Diagnosis. In Press. 

HEWLETT. Manual of Bacteriology. 75 Illustrations. $3.00 
ROBERTS. Gynecological Pathology. Illus. Just Ready $0.00 
THAYER. Compend of General Pathology. Illustrated. 
Nearly Ready. .80; Interleaved, £i.co 
THAYER. Compend of Special Pathology. Illustrated. 

Nearly Ready. .80 ; Interleaved, #1.00 
VIRCHOW. Post-Mortem Examinations. 3d Edition. .75 
WHITACRE. Laboratory Text-Book of Pathology. With 
121 Illustrations. $1.50 

WILLIAMS. Bacteriology. A Manual for Students. 90 Illus- 
trations. 2d Edition, Revised. Just Ready. $1.50 

PHARMACY. 

Special Catalogue of Books on Pharmacy sent free upon application. 

COBLENTZ. Manual of Pharmacy. A Complete Text-Book 
by the Professor in the New York College of Pharmacy. 2d Edition, 
Revised and Enlarged. 437 Illus. Cloth, $3. 50; Sheep, $4.50 

COBLENTZ. Volumetric Analysis. Illustrated. In Press. 

BEASLEY. Book of 3100 Prescriptions. Collected from the 
Practice of the Most Eminent Physicians and Surgeons — English, 
French, and American. A Compendious History of the Materia 
Medica, Lists of the Doses of all the Officinal and Established Pre- 
parations, an Ipdex of Diseases and their Remedies. 7th Ed. $2 .00 



MEDICAL BOOKS. 17 

BEASLEY. Druggists' General Receipt Book. Comprising 
a Copious Veterinary Formulary, Recipes in Patent and Proprietary 
Medicines, Druggists' Nostrums, etc. ; Perfumery and Cosmetics, 
Beverages, Dietetic Articles and Condiments, Trade Chemicals, 
Scientific Processes, and many Useful Tables, ioth Ed. $2.00 

BEASLEY. Pharmaceutical Formulary. A Synopsis of the 
British, French, German, and United States Pharmacopoeias. Com- 
prising Standard and Approved Formulae for the Preparations and 
Compounds Employed in Medicine. 12th Edition. $2.00 

PROCTOR. Practical Pharmacy. 3d Edition, with Illustrations 
and Elaborate Tables ot Chemical Solubilities, etc. $3.00 

ROBINSON. Latin Grammar of Pharmacy and Medicine. 

3d Edition. With elaborate Vocabularies. $*-75 

SAYRE. Organic Materia Medica and Pharmacognosy. An 

Introduction to the Study of the Vegetable Kingdom and the Vege- 
table and Animal Drugs. Comprising the Botanical and Physical 
Characteristics, Source, Constituents, and Pharmacopeial Prepar- 
ations, Insects Injurious to Drugs, and Parmacal Botany. With 
sections on Histology and Microtechnique, by W. C. Stevens. 
374 Illustrations. Second Edition. Cloth, $4.50 

SCOVILLE. The Art of Compounding. Second Edition, Re- 
vised and Enlarged. Cloth, #2.50 

STEWART. Compend of Pharmacy. Based upon " Reming- 
ton's Text-Book of Pharmacy." 5th Edition, Revised in Accord- 
ance with the U. S. Pharmacopoeia, 1890. Complete Tables of 
Metric and English Weights and Measures. .80; Interleaved, $1.00 

TAVERA. Medicinal Plants of the Philippines, 'just Ready. 

$2.00 

UNITED STATES PHARMACOPCEIA. 7 th Decennial Revision. 
Cloth, $2.50 (postpaid, $2.77) ; Sheep, $3.00 (postpaid, $3.27) ; Inter- 
leaved, $4.00 (postpaid, $4.50); Printed on one side of page only, 
unbound, $3.50 (postpaid, $3.90). 

Select Tables from the U. S. P. Being Nine of the Most Impor- 
tant and Useful Tables, Printed on Separate Sheets. .25 

POTTER. Hand-Book of Materia Medica, Pharmacy, and 
Therapeutics. 600 Prescriptions. 8th Ed. Clo., $5.00; Sh., $6.00 



PHYSIOLOGY. 

BIRCH. Practical Physiology. An Elementary Class Book. 
62 Illustrations. # x -75 

BRUBAKER. Compend of Physiology, ioth Edition, Revised 
and Enlarged. Illustrated. .80; Interleaved, $1. 00 

JONES. Outlines of Physiology. 96 Illustrations. Nearly Ready 

KIRKES. Handbook of Physiology. 17th Authorized Edition. 
Revised, Rearranged, and Enlarged. By Prof. W. D. Hallibur- 
ton, of Kings College, London. 681 Illustrations, some of which 
are in colors. Just Ready. Cloth, $3.00; Leather, $3.75 



18 SUBJECT CATALOGUE. 

LANDOIS. A Text-Book of Human Physiology, Including 
Histology and Microscopical Anatomy, with Special Reference to 
the Requirements of Practical Medicine. 5th American, translated 
from the 9th German Edition, with Additions by Wm. Stirling, 
m.d.,d.sc. 845 Illus., many of which are printed in colors. In Press. 

STARLING. Elements of Human Physiology. 100 Ills. $1.00 

STIRLING. Outlines of Practical Physiology. Including 
Chemical and Experimental Physiology, with Special Reference to 
Practical Medicine. 3d Edition. 289 Illustrations. $2.00 

TYSON. Cell Doctrine. Its History and Present State. $1.50 



PRACTICE. 

BEALE. On Slight Ailments; their Nature and Treatment. 

2d Edition, Enlarged and Illustrated. $1.25 

FAGGE. Practice of Medicine. 4th Edition, by P. H. Pye- 
Smith, m.d. 2 Volumes. In Press. 

FOWLER. Dictionary of Practical Medicine. By various 
writers. An Encyclopaedia of Medicine. Clo.,$3.oo; Half Mor. $4.00 
GOULD AND PYLE. Cyclopedia of Practical Medicine and 
Surgery. A Concise Reference Handbook, Alphabetically 
Arranged, with particular Reference to Diagnosis and Treatment. 
Edited by Drs. Gould and Pyle, Assisted by 72 Special Con- 
tributors. Illustrated, one volume. Large Square Octavo, Uniform 
with " Gould's Illustrated Dictionary." 

Sheep or Half Morocco, $10.00; with Thumb Index, $11.00 
Half Russia, Thumb Index, $12.00 

4®=* Complete descriptive circular free upon application. 

HUGHES. Compend of the Practice of Medicine. 6th Edition, 
Revised and Enlarged. 

Part I. Continued, Eruptive, and Periodical Fevers, Diseases of the 
Stomach, Intestines, Peritoneum, Biliary Passages, Liver, Kid- 
neys, etc., and General Diseases, etc. 
Part II. Diseases of the Respiratory System, Circulatory System, 
and Nervous System; Diseases of the Blood, etc. 

Price of each part, .80; Interleaved, $1.00 

Physician's Edition. In one volume, including the above two 

parts, a Section on Skin Diseases, and an Index. 6th Revised 

Edition. 625 pp. Full Morocco, Gilt Edge, $2.25 

MURRAY. Rough Notes on Remedies. 4th Ed. Just Ready. 

$1.25 
TAYLOR. Practice of Medicine. 6th Edition. Just Ready. $4.00 
TYSON. The Practice of Medicine. By James Tyson, m.d., 
Professor of Medicine in the University of Pennsylvania. A Com- 
plete Systematic Text-book with Special Reference to Diagnosis and 
Treatment. 2d Edition, Enlarged and Revised. Colored Plates and 
125 other Illustrations. 1222 Pages. Cloth, $5.50 ; Leather, $6.50 



PRESCRIPTION BOOKS. 

BEASLEY. Book of 310c Prescriptions. Collected from the 
Practice of the Most Eminent Physicians and Surgeons — English, 
French, and American. A Compendious History of the Materia, 
Medica, Lists of the Doses of all Officinal and Established Prepara- 
tions, and an Index of Diseases and their Remedies. 7th Ed. $2.00 






MEDICAL BOOKS. 19 



BEASLEY. Druggists' General Receipt Book. Comprising 
a Copious Veterinary Formulary, Recipes in Patent and Proprie- 
tary Medicines, Druggists' Nostrums, etc. ; Perfumery, and Cos- 
metics, Beverages, Dietetic Articles and Condiments, Trade Chem- 
icals, Scientific Processes, and an Appendix of Useful Tables. 
10th Edition, Revised. $2.00 

BEASLEY. Pocket Formulary. A Synopsis of the British, French, 
German, and United States Pharmacopoeias and the chief unofficial 
Formularies. 12th Edition. $2.00 



SKIN. 

BULKLEY. The Skin in Health and Disease. Illustrated. .40 
CROCKER. Diseases of the Skin. Their Description, Pathol- 
ogy, Diagnosis, and Treatment, with Special Reference to the Skin 
Eruptions of Children. 92 Illus. 3d Edition. Preparing. 

SCHAMBERG. Diseases of the Skin. 2d Edition, Revised and 
Enlarged. 105 Illustrations. Being No. 16 ? Quiz-Compend? Series. 

Cloth, .80; Interleaved, $1.00 

VAN HARLINGEN. On Skin Diseases. A Practical Manual 
of Diagnosis and Treatment, with special reference to Differential 
Diagnosis. 3d Edition, Revised and Enlarged. With Formulae 
and 60 Illustrations, some of which are printed in colors. #2.75 

SURGERY AND SURGICAL DIS- 
EASES (see also Urinary Organs). 

BERRY. Diseases of the Thyroid Gland and Their Surgical 
Treatment. Illustrated. Just Ready. #4.00 

BUTLIN. Operative Surgery of Malignant Disease. 2d Edi- 
tion. Illustrated. Octavo. $4.50 

DEAVER. Surgical Anatomy. A Treatise on Human Anatomy 
in its Application to Medicine and Surgery. With about 400 very 
Handsome full-page Illustrations Engraved from Original Drawings 
made by special Artists from Dissections prepared for the purpose. 
Three Volumes. Royal Square Octavo. 

Cloth, $21.00; Half Morocco or Sheep, $24.00 ; Half Russia, $27.00 
Complete descriptive circular and special terms upon application. 

DEAVER. Appendicitis, Its Symptoms, Diagnosis, Pathol- 
ogy, Treatment, and Complications. Elaborately Illustrated 
with Colored Plates and other Illustrations. 2d Edition. $3-5° 

DULLES. What to Do First in Accidents and Poisoning. 
5th Edition. New Illustrations. $1.00 

FULLERTON. Surgical Nursing. 3d Edition. 69 Illus. $1.00 

HAMILTON. Lectures on Tumors. 3d Edition. $1.25 

HEATH. Minor Surgery and Bandaging. 12th Edition, Revised 
and Enlarged. 195 Illus., Formulae, Diet List, etc. Just Ready. $1.30 

HEATH. Injuries and Diseases of the Jaws. 4th Ed. $4.50 
HORWITZ. Compend of Surgery and Bandaging, including 
Minor Surgery, Amputations, Fractures, Dislocations, Surgical Dis- 
eases, and the Latest Antiseptic Rules, etc., with Differential Diagno- 
sis and Treatment. 5th Edition, very much Enlarged and Rear- 
ranged. 167 Illustrations, 98 Formulae. Clo., .80 ; Interleaved, $1.00 



20 SUBJECT CATALOGUE. 

JACOBSON. Operations of Surgery. Over 200 Illustrations. 

Cloth, $3.00; Leather, $4.00 

KEHR. Gall-Stone Disease. Translated by William Wotkyns 
Seymour, m.d. fust Ready. #2.50 

LANE. Surgery of the Head and Neck, no Illus. $5.00 

MACREADY. A Treatise on Ruptures. 24 Full-page Litho- 
graphed Plates and Numerous Wood Engravings. Cloth, #6.00 

MAKINS. Surgical Experiences in South Africa. 1899-1900. 
Illustrated, fust Ready. $4.00 

MAYLARD. Surgery of the Alimentary Canal. 97 Illustrations. 
2d Edition, Revised. $3-oo 

MOULLIN. Text-Book of Surgery. With Special Reference to 
Treatment. 3d American Edition. Revised and edited by John B. 
Hamilton, m.d., ll.d., Professor of the Principles of Surgery and 
Clinical Surgery, Rush Medical College, Chicago. 623 Illustrations, 
many of which are printed in colors. Cloth, #6.00; Leather, $7.00 

SMITH. Abdominal Surgery. Being a Systematic Description of 
all the Principal Operations. 224 Illus. 6th Ed. 2 Vols. Clo., $10.00 

VOSWINKEL. Surgical Nursing. Second Edition, Revised and 
Enlarged, n 1 Illustrations. $1.00 

WALSHAM. Manual of Practical Surgery. 7th Ed., Re- 
vised and Enlarged. 483 Engravings. 950 pages. $3-5o 

TEMPERATURE CHARTS, ETC. 

GRIFFITH. Graphic Clinical Chart for Recording Temper- 
ature, Respiration, Pulse, Day of Disease, Date, Age, Sex, 
Occupation, Name, etc. Printed in three colors. Sample copies 
free. Put up in loose packages of fifty, .50. Price to Hospitals, 500 
copies, $4.00 ; 1000 copies, $7.50. With name of Hospital printed 
on, 50 cts. extra. 

KEEN'S CLINICAL CHARTS. Seven Outline Drawings of the 
Body, on which may be marked the Course of Disease, Fractures, 
Operations, etc. Each Drawing may be had separately, twenty-five 
to pad, 25 cents. 

SCHREINER. Diet Lists. Arranged in the form of a chart. 
With Pamphlets of Specimen Dietaries. Pads of 50. .75 

THROAT AND NOSE (see also Ear). 

COHEN. The Throat and Voice. Illustrated. .40 

HALL. Diseases of the Nose and Throat. 2d Edition, Enlarged. 
Two Colored Plates and 80 Illustrations. Just Ready. $2.75 

HOLLOPETER. Hay Fever. Its Successful Treatment. $1.00 

KNIGHT. Diseases of the Throat. A Manual for Students. 
Illustrated. Nearly Ready. 

LAKE. Laryngeal Phthisis, or Consumption of the Throat. 
Colored Illustrations. Just Ready, $2 00 

MACKENZIE. Pharmacopoeia of the London Hospital for 
Dis. of the Throat. 5th Ed., Revised by Dr. F. G. Harvey. $1.00 

McBRIDE. Diseases of the Throat, Nose, and Ear. With col- 
ored Illustrations from original drawings. 3d Edition. $7.00 

POTTER. Speech and its Defects. Considered Physiologically, 
Pathologically, and Remedially. $1.00 

SHEILD. Nasal Obstructions. Illustrated. Just Ready. $1.50 

URINE AND URINARY ORGANS. 

ACTON. The Functions and Disorders of the Reproductive 
Organs in Childhood, Youth, Adult Age, and Advanced Life, 

Considered in their Physiological, Social, and Moral Relations. 
8th Edition. $1.75 



MEDICAL BOOKS. 21 



BEALE. One Hundred Urinary Deposits. On eight sheets, 
for the Hospital, Laboratory, or Surgery. Paper, $2.00 

HOLLAND. The Urine, the Gastric Contents, the Common 
Poisons, and the Milk. Memoranda, Chemical and Microscopi- 
cal, for Laboratory Use. Illustrated and Interleaved. 6th Ed. #1.00 

KLEEN. Diabetes and Glycosuria. $2.50 

MEMMINGER. Diagnosis by the Urine. 2d Ed. 24 Illus. $1.00 

MORRIS. Renal Surgery, with Special Reference to Stone in the 
Kidney and Ureter and to the Surgical Treatment of Calculous 
Anuria. Illustrated. $2.00. 

MOULLIN. Enlargement of the Prostate. Its Treatment and 
Radical Cure. 2d Edition. Illustrated. $i-75 

MOULLIN. Inflammation of the Bladder and Urinary Fever. 
Octavo. $1.50 

SCOTT. The Urine. Its Clinical and Microscopical Examination. 
41 Lithographic Plates and other Illustrations. Quarto. Cloth, #5.00 

TYSON. Guide to Examination of the Urine. For the Use of 
Physicians and Students. With Colored Plate and Numerous Illus- 
trations engraved on wood. 9th Edition, Revised. $1.25 

VAN NUYS. Chemical Analysis of Urine. 39 Illus. $1.00 



VENEREAL DISEASES. 

GOWERS. Syphilis and the Nervous System. $1.00 

STURGIS AND CABOT. Student's Manual of Venereal 

Diseases. 7th Revised and Enlarged Ed. i2mo. Just Ready. #1.25 



VETERINARY. 

BALLOU. Veterinary Anatomy and Physiology. 29 Graphic 
Illustrations. .80; Interleaved, $1.00 



WOMEN, DISEASES OF. 

BISHOP. Uterine Fibromyomata. Their Pathology, Diagnosis, 
and Treatment. Illustrated. Just Ready. Cloth, #3 50 

BYFORD (H. T.). Manual of Gynecology. Second Edition, 
Revised and Enlarged by 100 pages. 341 Illustrations. $3.00 

DUHRSSEN. A Manual of Gynecological Practice. 105 
Illustrations. #1.50 

FULLERTON. Surgical Nursing. 3d Edition, Revised and 
Enlarged. 69 Illustrations. $1.00 

LEWERS. Diseases of Women. 146 Illus. 5th Ed. #2.50 

MONTGOMERY. Practical Gynecology. A Complete Sys- 
tematic Text-Book. 527 Illustrations. Cloth, $5.00; Leather, $6.00 

ROBERTS. Gynecological Pathology. With many Handsome 
Illustrations. Just Ready. 

WELLS. Compend of Gynecology. Illustrated. 2d Edition. 

. 80 ; Interleaved, $1 . 00 



22 SUBJECT CATALOGUE. 

COMPENDS. 



From The Southern Clinic. 

" We know of no series of books issued by any house that so fully 
meets our approval as these ?Quiz-Compends?. They are well ar- 
ranged, full, and concise, and are really the best line of text-books that 
could be found for either student or practitioner." 



BLAKISTON'S PQUIZ-COMPENDS? 

The Best Series of Manuals for the Use of Students. 
Price of each, Cloth, .80. Interleaved, for taking Notes, $1.00. 

4^" These Compends are based on the most popular text-books 
and the lectures of prominent professors, and are kept constantly re- 
vised, so that they may thoroughly represent the present state of the 
subjects upon which they treat. 

J^" The authors have had large experience as Quiz-Masters and 
attaches of colleges, and are well acquainted with the wants of students. 

Jfc5~ They are arranged in the most approved [form, thorough and 
concise, containing over 6oo fine illustrations, inserted wherever they 
could be used to advantage. 

M&- Can be used by students of any college. 

4^* They contain information nowhere else collected in such a 
condensed, practical shape. Illustrated Circular free. 

No. i. POTTER. HUMAN ANATOMY. Sixth Revised and 
Enlarged Edition. Including Visceral Anatomy. Can be used 
with either Morris's or Gray's Anatomy. 117 Illustrations and 16 
Lithographic Plates of Nerves and Arteries, with Explanatory 
Tables, etc. By Samuel O. L. Potter, m.d., Professor of the 
Practice of Medicine, College of Physicians and Surgeons, San 
Francisco ; Brigade Surgeon, U. S. Vol. 

No. 2. HUGHES. PRACTICE OF MEDICINE. Part I. Sixth 
Edition, Enlarged and Improved. By Daniel E. Hughes, m.d., 
Physician-in-Chief, Philadelphia Hospital, late Demonstrator of 
Clinical Medicine, Jefferson Medical College, Phila. 

No. 3. HUGHES. PRACTICE OF MEDICINE. Part II. 
Sixth Edition, Revised and Improved. Same author as No. 2. 

No. 4. BRUBAKER. PHYSIOLOGY. Tenth Edition, with 
Illustrations and a table of Physiological Constants. Enlarged 
and Revised. By A. P. Brubaker, m.d., Professor of Physiology 
and General Pathology in the Pennsylvania College of Dental 
Surgery ; Adjunct Professor of Physiology, Jefferson Medical 
College, Philadelphia, etc. 

No. 5. LANDIS. OBSTETRICS. Seventh Edition. By Henry G. 
Landis, m.d. Revised and Edited by Wm. H. Wells, m.d., 
Demonstrator of Clinical Obstetrics, Jefferson Medical College, 
Philadelphia. Enlarged. 52 Illustrations. 

No. 6. POTTER. MATERIA MEDICA, THERAPEUTICS, 
AND PRESCRIPTION WRITING. Sixth Revised Edition 
(U. S. P. 1890). By Samuel O. L. Potter, m.d., Professor of 
Practice, College of Physicians and Surgeons, San Francisco; 
Brigade Surgeon, U. S. Vol. 



MEDICAL BOOKS. 23 

PQUIZ-COMPENDS ?— Continued. 

No. 7. WELLS. GYNECOLOGY. Second Edition. ByW M .H. 
Wells, m.d., Demonstrator of Clinical Obstetrics, Jefferson 
Medical College, Philadelphia. 140 Illustrations. 

No. 8. GOULD AND PYLE. DISEASES OF THE EYE 
AND REFRACTION. Second Edition. Including Treatment 
and Surgery, and a Section on Local Therapeutics. By George 
M. Gould, m.d., and W. L. Pyle, m.d. With Formulae, Glossary 
Tables, and 109 Illustrations, several of which are Colored. 

No. 9. HORWITZ. SURGERY, Minor Surgery, and Bandag- 
ing. Fifth Edition, Enlarged and Improved. By Orvillb 
Horwitz, b. s., m.d., Clinical Professor of Genito-Urinary Surgery 
and Venereal Diseases in Jefferson Medical College ; Surgeon to 
Philadelphia Hospital, etc. With 98 Formulae and 71 Illustrations. 

No. 10. LEFFMANN. MEDICAL CHEMISTRY. Fourth 

Edition. Including Urinalysis, Animal Chemistry, Chemistry of 
Milk, Blood, Tissues, the Secretions, etc. By Henry Leffmann, 
m.d., Professor of Chemistry in the Woman's Medical College of 
Penna ; Pathological Chemist, Jefferson Medical College Hospital. 
No. 11. STEWART. PHARMACY. Fifth Edition. Based upon 
Prof. Remington's Text-Book of Pharmacy. By F. E. Stewart, 
m.d., ph.g., late Quiz-Master in Pharmacy and Chemistry, Phila- 
delphia College of Pharmacy ; Lecturer at Jefferson Medical 
College. Carefully revised in accordance with the new U. S. P. 

No. 12. BALLOU. VETERINARY ANATOMY AND PHY- 
SIOL9GY. Illustrated. By Wm. R. Ballou, m.d., Professor 
of Equine Anatomy at New York College of Veterinary Surgeons ; 
Physician to Bellevue Dispensary, etc. 29 graphic Illustrations 

No. 13. WARREN. DENTAL PATHOLOGY AND DEN- 
TAL MEDICINE. Third Edition, Illustrated. Containing 
a Section on Emergencies. By Geo. W. Warren, d.d.s., Chiei 
ot Clinical Staff, Pennsylvania College of Dental Surgery. 

No. 14. HATFIELD. DISEASES OF CHILDREN. Second 
Edition. Colored Plate. By Marcus P. Hatfield, Profes- 
sor of Diseases of Children, Chicago Medical College. 

No. 15. THAYER. GENERAL PATHOLOGY. By A. E. 

Thayer, m.d., Cornell University Medical College. Illustrated. 

No. 16. SCHAMBERG. DISEASES OF THE SKIN. Second 
Edition. By Jay F. Schamberg, m.d., Professor of Diseases of 
the Skin, Philadelphia Polyclinic. Second Edition, Revised and 
Enlarged. 105 handsome Illustrations. 

No. 17. CUSHING. HISTOLOGY. By H. H. Cushing, m.d., 
Demonstrator of Histology, Jefferson Medical College, Philadel- 
phia. Illustrated. 

No. 18. THAYER. SPECIAL PATHOLOGY. Illustrated. By 
same Author as No. 15. 

Price, each, Cloth, .80. Interleaved, for taking Notes, $1.00. 

Careful attention has been given to the construction of each sentence, 
and while the books will be found to contain an immense amount of 
knowledge in small space, they will likewise be found easy reading ; 
there is no stilted repetition of words ; the style is clear, lucid, and dis- 
tinct. The arrangement of subjects is systematic and thorough ; there 
Is a reason for every word. They contain over 600 illustrations. 



NOV 18 1901 

THE STANDARD TEXT-BOOK 

Morris* Anatomy 

SECOND EDITION 

Rewritten* Revised* Improved 

WITH MANY NEW ILLUSTRATIONS 



Has been recommended as a text-book at more than 
seventy of the most prominent medical schools in the United 
States and Canada, and is considered by al] anatomists as a 
standard authority. It contains many features of special 
advantage to students. A complete Text-book. Edited by 
Henry Morris, f.r.c.s., Surgeon to, and Lecturer on 
Anatomy at, Middlesex Hospital, assisted by J. Bland 
Sutton, f.r.c.s., J. H. Davies-Colley, f.r.c.s., Wm. J. 
Walsham, f.r.c.s., H. St. John Brooks, m»d., R. Mar- 
cus Gunn, f.r.c.s., Arthur Hensman, f.r.c.s., Fred- 
erick Treves, f.r.c.s., William Anderson, f.r.c.s., 
Prof. W. H. A. Jacobson, and Arthur Robinson, m.r.c.s. 

Octavo. With 790 Illustrations, of which a large number 
are printed in colors 

CLOTH, $6.00; LEATHER, $7.00 



i{ The ever-growing popularity of the book with teach- 
ers and students is an index of its value, and it may safely 
be recommended to all interested." — From The Medical 
Record, New York. 

"Of all the text-books of moderate size on human 
anatomy in the English language, Morris is undoubtedly 
the most up-to-date and accurate." — From The Philadel- 
phia Medical Journal. 

THUMB INDEX IN EACH COPY 



NOV 26 lOOl 



NOV 18 190S 



